An 8.9-magnitude earthquake hit northern Japan early Friday, triggering a tsunami that sent a wave filled with boats and houses toward land.
An estimated 170,000 people have been evacuated from the area around a quake-damaged nuclear power station in north-east Japan that was hit by an explosion, the UN atomic watchdog says.
A building housing a reactor was destroyed in Saturday's blast at the Fukushima 1 plant.The authorities said the reactor itself was intact inside its steel container.
Friday's devastating earthquake and tsunami is believed to have left more than 1,000 people dead.
The authorities are stepping up relief efforts as the scale of the tragedy becomes clear.
Officials announced that the number of troops helping with rescue work in the region would be doubled to 100,000.
The BBC's Damian Grammaticas in the coastal city of Sendai says the scenes of devastation are astonishing.
He says giant shipping containers have been swept inland and smashed against buildings, and fires are still burning close to the harbour.
Police said between 200 and 300 bodies were found in just one ward of the city.
The town of Rikuzentakada, Iwate prefecture, was almost completely submerged. Japanese broadcaster NHK reported that soldiers had found hundreds of bodies there.
NHK reports that in the port of Minamisanriku, Miyagi, the authorities say that about 7,500 people were evacuated to 25 shelters after Friday's quake but they have been unable to contact the town's other 10,000 inhabitants.
A local official in the town of Futaba said more than 90% of the houses in three coastal communities had been washed away by the tsunami. The scale of the devastation is immense.
"The tsunami was unbelievably fast," said Koichi Takairin, a 34-year-old truck driver who was inside his four-ton rig when the wave hit Sendai. "Smaller cars were being swept around me. All I could do was sit in my truck."
More than 215,000 people are said to be living in 1,350 temporary shelters in five prefectures.
International disaster relief teams are being sent to Japan, with the UN helping to co-ordinate the operation.
President Barack Obama has pledged US assistance. One US aircraft carrier that was already in Japan will help with rescue and relief efforts, and a second is on its way.
Japan's worst previous earthquake was of 8.3 magnitude and killed 143,000 people in Kanto in 1923. A magnitude 7.2 quake in Kobe killed 6,400 people in 1995.
Japan was battered by a 10-meter tsunami that swept everything in its path, including houses, cars and farm buildings, following the biggest quake in 140 years.
Japan confronted devastation along its northeastern coast on Saturday, with fires raging and parts of some cities under water after a massive earthquake and tsunami that likely killed at least 1,000 people. Daybreak was expected to reveal the full extent of the death and damage from Friday's 8.9 magnitude earthquake and the 10-metre high tsunami it sent surging into cities and villages, sweeping away everything in its path.
In one of the worst-hit residential areas, people buried under rubble could be heard calling out "help" and "when are we going to be rescued", Kyodo news agency reported.
The government warned there could be a small radiation leak from a nuclear reactor whose cooling system was knocked out by the quake. Prime Minister Naoto Kan ordered an evacuation zone around the plant be expanded to 10 km (6 miles) from 3 km. Some 3,000 people had earlier been moved out of harm's way.
Underscoring concerns about the Fukushima plant, 240 km (150 miles) north of Tokyo, U.S. officials said Japan had asked for coolant to avert a rise in the temperature of its nuclear rods, but ultimately handled the matter on its own. Officials said a leak was still possible because pressure would have to be released. The unfolding natural disaster prompted offers of search and rescue help from 45 countries.
China said rescuers were ready to help with quake relief while President Barack Obama told Japanese Prime Minister Naoto Kan the United States would assist in any way.
"This is likely to be a humanitarian relief operation of epic proportions," Japan expert Sheila Smith of the U.S.-based Council on Foreign Relations wrote in a commentary.
The northeastern Japanese city of Kesennuma, with a population of 74,000, was hit by widespread fires and one-third of the city was under water, Jiji news agency said on Saturday.
The airport in the city of Sendai, home to one million people, was on fire, it added.
TV footage from Friday showed a muddy torrent of water carrying cars and wrecked homes at high speed across farmland near Sendai, 300 km (180 miles) northeast of Tokyo. Ships had been flung onto a harbour wharf, where they lay helplessly on their side.
Boats, cars and trucks were tossed around like toys in the water after a small tsunami hit the town of Kamaichi in northern Japan. Kyodo news agency reported that contact had been lost with four trains in the coastal area.
Japanese politicians pushed for an emergency budget to fund relief efforts after Kan asked them to "save the country", Kyodo news agency reported. Japan is already the most heavily indebted major economy in the world, meaning any funding efforts would be closely scrutinised by financial markets.
Domestic media said the death toll was expected to exceed 1,000, most of whom appeared to have drowned by churning waters.
The extent of the destruction along a lengthy stretch of coastline suggested the death toll could rise significantly. Even in a nation accustomed to earthquakes, the devastation was shocking.
"A big area of Sendai city near the coast, is flooded. We are hearing that people who were evacuated are stranded," said Rie Sugimoto, a reporter for NHK television in Sendai.
"About 140 people, including children, were rushed to an elementary school and are on the rooftop but they are surrounded by water and have nowhere else to go."
Japan has prided itself on its speedy tsunami warning system, which has been upgraded several times since its inception in 1952, including after a 7.8 magnitude quake triggered a 30-metre high wave before a warning was given.
The country has also built countless breakwaters and floodgates to protect ports and coastal areas, although experts said they might not have been enough to prevent disasters such as the one that struck on Friday.
In Tokyo, many residents who had earlier fled swaying buildings slept in their offices after public transport was shut down. Many subways in Tokyo later resumed operation but trains did not run.
"I was unable stay on my feet because of the violent shaking. The aftershocks gave us no reprieve. Then the tsunamis came when we tried to run for cover. It was the strongest quake I experienced," a woman with a baby on her back told television in northern Japan.
Fires across the coast
The quake, the most powerful since Japan started keeping records 140 years ago, sparked at least 80 fires in cities and towns along the coast, Kyodo said.
Other Japanese nuclear power plants and oil refineries were shut down and one refinery was ablaze.
Auto plants, electronics factories and refineries shut, roads buckled and power to millions of homes and businesses was knocked out. Several airports, including Tokyo's Narita, were closed and rail services halted. All ports were shut. The central bank said it would cut short a two-day policy review scheduled for next week to one day on Monday and promised to do its utmost to ensure financial market stability.
The disaster occurred as the world's third-largest economy had been showing signs of reviving from an economic contraction in the final quarter of last year. It raised the prospect of major disruptions for many key businesses and a massive repair bill running into tens of billions of dollars.
The tsunami alerts revived memories of the giant waves that struck Asia in 2004.
Warnings were issued for countries to the west of Japan and across the Pacific as far away as Colombia and Peru, but the tsunami dissipated as it sped across the ocean and worst fears in the Americas were not realised.
The earthquake was the fifth most powerful to hit the world in the past century.
"The building shook for what seemed a long time and many people in the newsroom grabbed their helmets and some got under their desks," Reuters correspondent Linda Sieg said in Tokyo. "It was probably the worst I have felt since I came to Japan more than 20 years ago."
The quake surpasses the Great Kanto quake of Sept. 1, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history. Economic damage from the 2004 Indian Ocean tsunami was estimated at about $10 billion.
Earthquakes are common in Japan, one of the world's most seismically active areas.
The 8.9-magnitude earthquake and coastline-devouring tsunami that hit Japan has led 49 countries, the European Union and even the International Atomic Energy Agency to band together and offer relief to the devastated island nation.
With Japan's death toll at 686 people, the international relief effort has been spurred by the stark, globally televised videos of homes and offices rattled to near collapse and entire waterfront communities being washed away by a rising ocean.
The international community's assistance complemented the United States' expansive relief mission, which includes supplies, several warships, search-and-rescue teams, radiation-contamination specialists, and two officials from the U.S. Nuclear Regulatory Commission with expertise in boiling water nuclear reactors.
On Sunday, the nuclear-powered aircraft carrier USS Ronald Reagan arrived off the coast of Honshu to support Japanese forces in disaster relief operations, the U.S. Department of Defense said in a statement.
In addressing one of the bigger potential threats, the international atomic agency's Incident and Emergency Centre has offered technical assistance to Japan in the wake of an explosion at the Fukushima Daiichi nuclear plant. An evacuation order for a 20-kilometer (12.4-mile) radius around the plant is affecting tens of thousands of people.
In one of the worst-hit residential areas, people buried under rubble could be heard calling out "help" and "when are we going to be rescued", Kyodo news agency reported.
The government warned there could be a small radiation leak from a nuclear reactor whose cooling system was knocked out by the quake. Prime Minister Naoto Kan ordered an evacuation zone around the plant be expanded to 10 km (6 miles) from 3 km. Some 3,000 people had earlier been moved out of harm's way.
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China said rescuers were ready to help with quake relief while President Barack Obama told Japanese Prime Minister Naoto Kan the United States would assist in any way.
"This is likely to be a humanitarian relief operation of epic proportions," Japan expert Sheila Smith of the U.S.-based Council on Foreign Relations wrote in a commentary.
The northeastern Japanese city of Kesennuma, with a population of 74,000, was hit by widespread fires and one-third of the city was under water, Jiji news agency said on Saturday.
The airport in the city of Sendai, home to one million people, was on fire, it added.
TV footage from Friday showed a muddy torrent of water carrying cars and wrecked homes at high speed across farmland near Sendai, 300 km (180 miles) northeast of Tokyo. Ships had been flung onto a harbour wharf, where they lay helplessly on their side.
Boats, cars and trucks were tossed around like toys in the water after a small tsunami hit the town of Kamaichi in northern Japan. Kyodo news agency reported that contact had been lost with four trains in the coastal area.
Japanese politicians pushed for an emergency budget to fund relief efforts after Kan asked them to "save the country", Kyodo news agency reported. Japan is already the most heavily indebted major economy in the world, meaning any funding efforts would be closely scrutinised by financial markets.
Domestic media said the death toll was expected to exceed 1,000, most of whom appeared to have drowned by churning waters.
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"A big area of Sendai city near the coast, is flooded. We are hearing that people who were evacuated are stranded," said Rie Sugimoto, a reporter for NHK television in Sendai.
"About 140 people, including children, were rushed to an elementary school and are on the rooftop but they are surrounded by water and have nowhere else to go."
Japan has prided itself on its speedy tsunami warning system, which has been upgraded several times since its inception in 1952, including after a 7.8 magnitude quake triggered a 30-metre high wave before a warning was given.
The country has also built countless breakwaters and floodgates to protect ports and coastal areas, although experts said they might not have been enough to prevent disasters such as the one that struck on Friday.
In Tokyo, many residents who had earlier fled swaying buildings slept in their offices after public transport was shut down. Many subways in Tokyo later resumed operation but trains did not run.
"I was unable stay on my feet because of the violent shaking. The aftershocks gave us no reprieve. Then the tsunamis came when we tried to run for cover. It was the strongest quake I experienced," a woman with a baby on her back told television in northern Japan.
Fires across the coast
The quake, the most powerful since Japan started keeping records 140 years ago, sparked at least 80 fires in cities and towns along the coast, Kyodo said.
Other Japanese nuclear power plants and oil refineries were shut down and one refinery was ablaze.
The disaster occurred as the world's third-largest economy had been showing signs of reviving from an economic contraction in the final quarter of last year. It raised the prospect of major disruptions for many key businesses and a massive repair bill running into tens of billions of dollars.
The tsunami alerts revived memories of the giant waves that struck Asia in 2004.
Warnings were issued for countries to the west of Japan and across the Pacific as far away as Colombia and Peru, but the tsunami dissipated as it sped across the ocean and worst fears in the Americas were not realised.
The earthquake was the fifth most powerful to hit the world in the past century.
"The building shook for what seemed a long time and many people in the newsroom grabbed their helmets and some got under their desks," Reuters correspondent Linda Sieg said in Tokyo. "It was probably the worst I have felt since I came to Japan more than 20 years ago."
The quake surpasses the Great Kanto quake of Sept. 1, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history. Economic damage from the 2004 Indian Ocean tsunami was estimated at about $10 billion.
Earthquakes are common in Japan, one of the world's most seismically active areas.
Helicopters land on the USS Tortuga in the Sea of Japan on Saturday as the U.S. military prepares to deliver aid.
- The United Kingdom is among those sending search-and-rescue teams
- Korea is dispatching rescue dogs
- The International Atomic Energy Agency is offering its nuclear experts
With Japan's death toll at 686 people, the international relief effort has been spurred by the stark, globally televised videos of homes and offices rattled to near collapse and entire waterfront communities being washed away by a rising ocean.
The international community's assistance complemented the United States' expansive relief mission, which includes supplies, several warships, search-and-rescue teams, radiation-contamination specialists, and two officials from the U.S. Nuclear Regulatory Commission with expertise in boiling water nuclear reactors.
On Sunday, the nuclear-powered aircraft carrier USS Ronald Reagan arrived off the coast of Honshu to support Japanese forces in disaster relief operations, the U.S. Department of Defense said in a statement.
In addressing one of the bigger potential threats, the international atomic agency's Incident and Emergency Centre has offered technical assistance to Japan in the wake of an explosion at the Fukushima Daiichi nuclear plant. An evacuation order for a 20-kilometer (12.4-mile) radius around the plant is affecting tens of thousands of people.
On Saturday, the United Kingdom said it was sending a team of 59 fire service search-and-rescue specialists, two rescue dogs and a medical support team, according to the Foreign and Commonwealth Office.
With a scheduled arrival on Sunday, the crew will immediately join the international search for survivors in shattered and inundated communities, the British office said.
The teams will take up to 11 tonnes of rescue equipment, including heavy lifting and cutting equipment to extract people trapped in debris, the government said.
The UK foreign office also dispatched a 10-member consular response team, including British Red Cross workers, to Japan on Saturday morning, the government said.
South Korea is sending two rescue dogs, two handlers and three assistants to carry out what are expected to be dramatic searches of people inside collapsed structures. The rescue teams were scheduled to arrive Saturday, Japan's Ministry of Foreign Affairs said in a written statement.
In China, Premier Wen Jiabao, who expressed "deep sympathy" to the Japanese government and people, made a formal offer of assistance. Members of the country's international rescue team were ready to depart for Japan if needed, Chen Jianmin, director of the China Earthquake Administration, told the government's Xinhua News Agency.
The United States is providing as many 11 warships, with their helicopters, to assist Japanese authorities in rescue and recovery missions.
The U.S. Agency for International Development was dispatching two urban search-and-rescue teams, one from Fairfax County, Virginia, and the second from Los Angeles County -- totaling 150 people and 12 canines trained to find survivors. They are scheduled to arrive Monday morning in Japan.
CONCERN ABOUT FOOD AND FUEL IN WAKE OF JAPAN'S DISASTERS
Long lines at grocery stores and gas stations along with continued aftershocks and power outages greeted many in Japan on Sunday morning, nearly two days after the devastating earthquake and tsunami that left hundreds dead and missing.
Supplies of food and gas were running out in Sendai, the northern coastal city close to the epicenter of Friday's quake. Those who survived the earthquake and chose to remain in the city were enduring two-hour waits at the supermarket, according to a CNN iReporter in Sendai with the username joeyjenkins.
"They have waited for I don't even know how long to get gas, as the gas station manually pumps the gas since there is no electricity," joeyjenkins wrote, adding they were without power until early Sunday.
Schools and hospitals and Sendai have been turned into shelters, and volunteers were handing out bottles of water, CNN correspondent Kyung Lah reported from the city.
Fears of power outages in Tokyo, about 200 miles south, sparked a run on flashlights, said iReporter Jessica Tekawa, 26.
"I think last night, there must have been something on the news about a power outage," she told CNN, "because when we went, with my friend, we were trying to get flashlights and they were sold out everywhere."
Water, too, was sold out in every store she went to after similar reports of possible water contamination, she said.
Kenneth Cukier, the Japan correspondent for The Economist magazine, said the government announced managed power cuts will start Monday in certain regions of the country -- including suburban areas of Tokyo -- to give businesses enough power to operate.
A seemingly endless barrage of aftershocks from Friday's 8.9-magnitude quake were still rattling nerves Sunday. The U.S. Geological Survey reported more than 140 such quakes -- magnitude 4.5 and higher, with the strongest coming at a 6.4 -- in, near, or off the east coast of the Japanese island.
The aftershocks are a "constant reminder of what's happened, and what could happen in the future," Wall Street Journal reporter Yoree Koh told CNN from Tokyo.
With a scheduled arrival on Sunday, the crew will immediately join the international search for survivors in shattered and inundated communities, the British office said.
The teams will take up to 11 tonnes of rescue equipment, including heavy lifting and cutting equipment to extract people trapped in debris, the government said.
The UK foreign office also dispatched a 10-member consular response team, including British Red Cross workers, to Japan on Saturday morning, the government said.
South Korea is sending two rescue dogs, two handlers and three assistants to carry out what are expected to be dramatic searches of people inside collapsed structures. The rescue teams were scheduled to arrive Saturday, Japan's Ministry of Foreign Affairs said in a written statement.
In China, Premier Wen Jiabao, who expressed "deep sympathy" to the Japanese government and people, made a formal offer of assistance. Members of the country's international rescue team were ready to depart for Japan if needed, Chen Jianmin, director of the China Earthquake Administration, told the government's Xinhua News Agency.
The United States is providing as many 11 warships, with their helicopters, to assist Japanese authorities in rescue and recovery missions.
The U.S. Agency for International Development was dispatching two urban search-and-rescue teams, one from Fairfax County, Virginia, and the second from Los Angeles County -- totaling 150 people and 12 canines trained to find survivors. They are scheduled to arrive Monday morning in Japan.
On Saturday, the Japanese foreign ministry listed the 49 countries extending offers of relief, in no particular order: Australia, Taiwan, the United States, South Korea, China, Mexico, Thailand, New Zealand, Israel, Singapore, Indonesia, Azerbaijan, India, Russia, Turkey, Germany, France, Belgium, Ukraine, Slovakia, United Arab Emirates, Switzerland, Hungary, Poland, Jordan, the United Kingdom, Chile, Spain, Greece, Hong Kong, Pakistan, Denmark, Serbia, Uruguay, Mongolia, Ecuador, Iran, Kyrgyz Republic, Malaysia, Argentine, Philippines, Canada, Italy, Sweden, Kosovo, Iceland, Norway, Romania, and Slovenia.
CONCERN ABOUT FOOD AND FUEL IN WAKE OF JAPAN'S DISASTERS
Long lines at grocery stores and gas stations along with continued aftershocks and power outages greeted many in Japan on Sunday morning, nearly two days after the devastating earthquake and tsunami that left hundreds dead and missing.
Supplies of food and gas were running out in Sendai, the northern coastal city close to the epicenter of Friday's quake. Those who survived the earthquake and chose to remain in the city were enduring two-hour waits at the supermarket, according to a CNN iReporter in Sendai with the username joeyjenkins.
"They have waited for I don't even know how long to get gas, as the gas station manually pumps the gas since there is no electricity," joeyjenkins wrote, adding they were without power until early Sunday.
Schools and hospitals and Sendai have been turned into shelters, and volunteers were handing out bottles of water, CNN correspondent Kyung Lah reported from the city.
Fears of power outages in Tokyo, about 200 miles south, sparked a run on flashlights, said iReporter Jessica Tekawa, 26.
"I think last night, there must have been something on the news about a power outage," she told CNN, "because when we went, with my friend, we were trying to get flashlights and they were sold out everywhere."
Water, too, was sold out in every store she went to after similar reports of possible water contamination, she said.
Kenneth Cukier, the Japan correspondent for The Economist magazine, said the government announced managed power cuts will start Monday in certain regions of the country -- including suburban areas of Tokyo -- to give businesses enough power to operate.
A seemingly endless barrage of aftershocks from Friday's 8.9-magnitude quake were still rattling nerves Sunday. The U.S. Geological Survey reported more than 140 such quakes -- magnitude 4.5 and higher, with the strongest coming at a 6.4 -- in, near, or off the east coast of the Japanese island.
The aftershocks are a "constant reminder of what's happened, and what could happen in the future," Wall Street Journal reporter Yoree Koh told CNN from Tokyo.
"People are wondering, could there be an aftershock that's greater than the original earthquake?" Tuchman said. "Each time you feel it, there's an element of fear."
The Japanese military was working in at least one neighborhood of Sendai on Sunday morning to search for anyone trapped in the rubble. "A few hundred" people were still unaccounted for in one part of town Sunday.
Reports from the National Institute of Geophysics and Volcanology in Italy estimated the 8.9-magnitude quake shifted the planet on its axis by nearly 4 inches (10 centimeters).
The temblor, which struck Friday afternoon near the east coast of Japan, killed hundreds of people, caused the formation of 30-foot walls of water that swept across rice fields, engulfed entire towns, dragged houses onto highways, and tossed cars and boats like toys. Some waves reached six miles (10 kilometers) inland in Miyagi Prefecture on Japan's east coast.
Japan is located along the Pacific "ring of fire," an area of high seismic and volcanic activity stretching from New Zealand in the South Pacific up through Japan, across to Alaska and down the west coasts of North and South America. The quake was "hundreds of times larger" than the 2010 quake that ravaged Haiti, said Jim Gaherty of the LaMont-Doherty Earth Observatory at Columbia University.
The Japanese quake was of similar strength to the 2004 earthquake in Indonesia that triggered a tsunami that killed over 200,000 people in more than a dozen countries around the Indian Ocean. "The tsunami that it sent out was roughly comparable in terms of size," Gaherty said. "[The 2004 tsunami] happened to hit some regions that were not very prepared for tsunamis ... we didn't really have a very sophisticated tsunami warning system in the Indian Ocean basin at the time so the damage was significantly worse."
The Japanese quake comes just weeks after a 6.3-magnitude earthquake struck Christchurch on February 22, toppling historic buildings and killing more than 150 people. The timeframe of the two quakes have raised questions whether the two incidents are related, but experts say the distance between the two incidents makes that unlikely.
Friday, 11 March: 1446 local time (0546 GMT)
The 8.9-magnitude earthquake strikes off the coast of Honshu island at a depth of about 24km. The tremor triggers the automatic shutdown of 11 of the nation's nuclear power reactors, including reactor units 1,2 and 3 at the Fukushima Daiichi power plant. Reactor units 4, 5 and 6 were undergoing routine inspections, so were not operating.
The quake causes the power station to be cut off from the national electricity grid. The plant's operators, Tokyo Electric Power Co (Tepco), find that the diesel-powered emergency generators for units 1 and 2 are not working and notify government officials.
1600: Japan's Nuclear and Industrial Safety Agency (Nisa) sets up an emergency headquarters to gather information on potential damage to the nation's 55 nuclear reactors.
1930: Chief Cabinet Secretary Yukio Edano announces that Prime Minister Naoto Kan has declared a "nuclear emergency status". Officials reassure people that this is standard procedure in events like this and no radioactive material has been detected in the area surrounding the power station.
Unit 1
The pressure is the result of the reactors residual "decay" heat causing the coolant, which is not being circulated, to evaporate.
The consequent increase in pressure in the coolant circuit can be controlled by pressure release valves, but this leads to an increase in pressure within the reactor building containment chamber.
Tepco says that the pressure inside reactor unit 1 is more than twice normal levels.
Saturday, 12 March: 0530 local time
In order to release some of the pressure inside the reactor unit, the decision is taken to vent some of the steam, which contains a small amount of radioactive material, into the air.
0819: An alarm alerts workers that the position of one control rod (used to halt the reactor) is unclear (whether it is fully inserted into the reactor or outside the reactor, allowing it to continue generating heat)
1009: Tepco confirms it has released a small amount of vapour into the atmosphere to reduce pressure in reactor unit 1.
1043: Control rod alarm stops, and all rods are confirmed as being fully inserted.
1058: In order to release some of pressure inside reactor unit 2, some steam was vented into the air. Again, this contains a small amount of radioactive material.
1530: TV cameras capture a massive explosion at the power station. The pictures appear to show that the outer structure of one of four buildings at the plant has collapsed. Tokyo Electric Power Co says four workers have been injured in the blast.
2000: Uncertainty surrounds what was the actual cause of the explosion, and what damaged was caused by the blast.
Chief Cabinet Secretary Yukio Edano confirms that the concrete building surrounding the steel reactor container has collapsed as a result of the blast, but the steel containment chamber itself had not been damaged.
Nausea and vomiting often begin within hours of exposure, followed by diarrhoea, headaches and fever.
After the first round of symptoms, there may be a brief period with no apparent illness, but this may be followed within weeks by new, more serious symptoms.
At higher levels of radiation, all of these symptoms may be immediately apparent, along with widespread - and potentially fatal - damage to internal organs.
Exposure to a radiation dose of four grays will typically kill about half of all healthy adults.
For comparison, radiation therapy for cancer typically involves several doses of between one and seven grays at a time.
Drugs are available that increase white blood-cell production to counter any damage that may have occurred to the bone marrow, and to reduce the risk of further infections due to immune-system damage.
There are also specific drugs that can help to reduce the damage to internal organs caused by radioactive particles.
The body responds by trying to repair this damage, but sometimes it is too severe or widespread to make repair possible. There is also a danger of mistakes in the natural repair process.
Regions of the body that are most vulnerable to radiation damage include the cells lining the intestine and stomach, and the blood-cell producing cells in the bone marrow.
The extent of the damage caused is dependent on how long people are exposed to radiation, and at what level.
The body has various processes for ensuring that cells do not become cancerous, and for replacing damaged tissue.
But the damage caused by exposure to radiation can completely disrupt these control processes, making it much more likely that cancer will result.
Failure to repair the damage caused by radiation properly can also result in changes - or mutations - to the body's genetic material, which are not only associated with cancer, but may also be potentially passed down to offspring, leading to deformities in future generations. These can include smaller head or brain size, poorly formed eyes, slow growth and severe learning difficulties.
Following the Chernobyl nuclear reactor accident in the Ukraine in 1986, the World Health Organization recorded a dramatic increase in thyroid cancer among children in the vicinity.
This was because the radioactive materials released during the accident contained high levels of radioactive iodine, a material that accumulates in the thyroid.
He said in those circumstances the only people likely to be at risk of serious health effects were nuclear workers at the plant or emergency workers exposed to high levels of radiation.
He said the top priority would be to evacuate people from the area and to make sure they did not eat contaminated food. The biggest risk was that radioactive iodine could get into their system, raising the risk of thyroid cancer.
To counter that risk people could be given tablets containing stable iodine which would prevent the body absorbing the radioactive version.
The Japanese military was working in at least one neighborhood of Sendai on Sunday morning to search for anyone trapped in the rubble. "A few hundred" people were still unaccounted for in one part of town Sunday.
The city was still littered with debris and standing water from the tsunami. Two to three miles inland, houses were destroyed or "simply gone," cars were stacked on top of each other, and brown mud covered the ground.
QUAKE MOVED JAPAN COAST 8 FEET, SHIFTED EARTH AXIS
The powerful earthquake that unleashed a devastating tsunami Friday appears to have moved the main island of Japan by 8 feet (2.4 meters) and shifted the Earth on its axis.
"At this point, we know that one GPS station moved (8 feet), and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass," said Kenneth Hudnut, a geophysicist with the U.S. Geological Survey (USGS).Reports from the National Institute of Geophysics and Volcanology in Italy estimated the 8.9-magnitude quake shifted the planet on its axis by nearly 4 inches (10 centimeters).
The temblor, which struck Friday afternoon near the east coast of Japan, killed hundreds of people, caused the formation of 30-foot walls of water that swept across rice fields, engulfed entire towns, dragged houses onto highways, and tossed cars and boats like toys. Some waves reached six miles (10 kilometers) inland in Miyagi Prefecture on Japan's east coast.
The quake was the most powerful to hit the island nation in recorded history and the tsunami it unleashed traveled across the Pacific Ocean, triggering tsunami warnings and alerts for 50 countries and territories as far away as the western coasts of Canada, the U.S. and Chile. The quake triggered more than 160 aftershocks in the first 24 hours -- 141 measuring 5.0-magnitude or more.
The quake occurred as the Earth's crust ruptured along an area about 250 miles (400 kilometers) long by 100 miles (160 kilometers) wide, as tectonic plates slipped more than 18 meters, said Shengzao Chen, a USGS geophysicist.
Japan is located along the Pacific "ring of fire," an area of high seismic and volcanic activity stretching from New Zealand in the South Pacific up through Japan, across to Alaska and down the west coasts of North and South America. The quake was "hundreds of times larger" than the 2010 quake that ravaged Haiti, said Jim Gaherty of the LaMont-Doherty Earth Observatory at Columbia University.
The Japanese quake was of similar strength to the 2004 earthquake in Indonesia that triggered a tsunami that killed over 200,000 people in more than a dozen countries around the Indian Ocean. "The tsunami that it sent out was roughly comparable in terms of size," Gaherty said. "[The 2004 tsunami] happened to hit some regions that were not very prepared for tsunamis ... we didn't really have a very sophisticated tsunami warning system in the Indian Ocean basin at the time so the damage was significantly worse."
The Japanese quake comes just weeks after a 6.3-magnitude earthquake struck Christchurch on February 22, toppling historic buildings and killing more than 150 people. The timeframe of the two quakes have raised questions whether the two incidents are related, but experts say the distance between the two incidents makes that unlikely.
"I would think the connection is very slim," said Prof. Stephan Grilli, ocean engineering professor at the University of Rhode Island.
explosion in one of its six reactor units. Amid growing concerns about radioactive material spreading into the surrounding environment, BBC News looks at the events that led to the blast.
The 8.9-magnitude earthquake strikes off the coast of Honshu island at a depth of about 24km. The tremor triggers the automatic shutdown of 11 of the nation's nuclear power reactors, including reactor units 1,2 and 3 at the Fukushima Daiichi power plant. Reactor units 4, 5 and 6 were undergoing routine inspections, so were not operating.
The quake causes the power station to be cut off from the national electricity grid. The plant's operators, Tokyo Electric Power Co (Tepco), find that the diesel-powered emergency generators for units 1 and 2 are not working and notify government officials.
1600: Japan's Nuclear and Industrial Safety Agency (Nisa) sets up an emergency headquarters to gather information on potential damage to the nation's 55 nuclear reactors.
1930: Chief Cabinet Secretary Yukio Edano announces that Prime Minister Naoto Kan has declared a "nuclear emergency status". Officials reassure people that this is standard procedure in events like this and no radioactive material has been detected in the area surrounding the power station.
Fukushima Daiichi power station
There are six reactors known as 'units' in the power station.Unit 1
- 439 MW Boiling Water Reactor (BWR); opened in 1971
- Automatically shut down
- Water level decreasing
- Pressure release implemented
- Explosion observed with unknown effect
- 760 MW BWR; opened in 1974
- Automatically shut down
- Water level lower but steady
- Preparations for pressure release
- 760 MW BWR; opened in 1976
- Automatically shut down
- Preparations for pressure release
- 760 MW BWR, opened in 1978
- Shut for periodic inspection
- 760 MW BWR; opened in 1978
- Shut for periodic inspection
- 1,067 MW BWR; opened in 1979
- Shut for periodic inspection
2100: Residents within a 3km radius of the power station are told to leave their homes, while those within a 10km radius are told to stay at home in case it is necessary to extend the evacuation area.
Following the automatic shutdown of the reactors, and the failure of emergency generators, pressure in the unit builds up as a result of the pumps in the cooling system not working properly.The pressure is the result of the reactors residual "decay" heat causing the coolant, which is not being circulated, to evaporate.
The consequent increase in pressure in the coolant circuit can be controlled by pressure release valves, but this leads to an increase in pressure within the reactor building containment chamber.
Tepco says that the pressure inside reactor unit 1 is more than twice normal levels.
Saturday, 12 March: 0530 local time
In order to release some of the pressure inside the reactor unit, the decision is taken to vent some of the steam, which contains a small amount of radioactive material, into the air.
0819: An alarm alerts workers that the position of one control rod (used to halt the reactor) is unclear (whether it is fully inserted into the reactor or outside the reactor, allowing it to continue generating heat)
1009: Tepco confirms it has released a small amount of vapour into the atmosphere to reduce pressure in reactor unit 1.
1043: Control rod alarm stops, and all rods are confirmed as being fully inserted.
1058: In order to release some of pressure inside reactor unit 2, some steam was vented into the air. Again, this contains a small amount of radioactive material.
1530: TV cameras capture a massive explosion at the power station. The pictures appear to show that the outer structure of one of four buildings at the plant has collapsed. Tokyo Electric Power Co says four workers have been injured in the blast.
2000: Uncertainty surrounds what was the actual cause of the explosion, and what damaged was caused by the blast.
Chief Cabinet Secretary Yukio Edano confirms that the concrete building surrounding the steel reactor container has collapsed as a result of the blast, but the steel containment chamber itself had not been damaged.
Japanese officials have ordered anyone living within 20km (12 miles) of the Fukushima nuclear power plant to evacuate the area.
A large explosion has occurred in one of its buildings and some radiation leakage has been detected. If the Japanese authorities act swiftly, they should be able to minimise the cost to human health. What are the immediate health effects of exposure to radiation?
Exposure to moderate levels can result in radiation sickness, which produces a range of symptoms.Nausea and vomiting often begin within hours of exposure, followed by diarrhoea, headaches and fever.
After the first round of symptoms, there may be a brief period with no apparent illness, but this may be followed within weeks by new, more serious symptoms.
At higher levels of radiation, all of these symptoms may be immediately apparent, along with widespread - and potentially fatal - damage to internal organs.
Exposure to a radiation dose of four grays will typically kill about half of all healthy adults.
For comparison, radiation therapy for cancer typically involves several doses of between one and seven grays at a time.
How is radiation sickness treated?
The first thing to do is to try to minimise further contamination by removing clothes and shoes, and gently washing the skin with soap and water.Drugs are available that increase white blood-cell production to counter any damage that may have occurred to the bone marrow, and to reduce the risk of further infections due to immune-system damage.
There are also specific drugs that can help to reduce the damage to internal organs caused by radioactive particles.
How does radiation have an impact on health?
Radioactive materials that decay spontaneously produce ionising radiation, which has the capacity to cause significant damage to the body's internal chemistry, breaking the chemical bonds between the atoms and molecules that make up our tissues.The body responds by trying to repair this damage, but sometimes it is too severe or widespread to make repair possible. There is also a danger of mistakes in the natural repair process.
Regions of the body that are most vulnerable to radiation damage include the cells lining the intestine and stomach, and the blood-cell producing cells in the bone marrow.
The extent of the damage caused is dependent on how long people are exposed to radiation, and at what level.
What are the most likely long-term health effects?
Cancer is the biggest long-term risk. Usually when the body's cells reach their "sell-by date" they commit suicide. Cancer results when cells lose this ability, and effectively become immortal, continuing to divide and divide in an uncontrolled fashion. The body has various processes for ensuring that cells do not become cancerous, and for replacing damaged tissue.
But the damage caused by exposure to radiation can completely disrupt these control processes, making it much more likely that cancer will result.
Failure to repair the damage caused by radiation properly can also result in changes - or mutations - to the body's genetic material, which are not only associated with cancer, but may also be potentially passed down to offspring, leading to deformities in future generations. These can include smaller head or brain size, poorly formed eyes, slow growth and severe learning difficulties.
Are children at greater risk?
Potentially yes. Because they are growing more rapidly, more cells are dividing, and so the potential for things to go wrong is greater.Following the Chernobyl nuclear reactor accident in the Ukraine in 1986, the World Health Organization recorded a dramatic increase in thyroid cancer among children in the vicinity.
This was because the radioactive materials released during the accident contained high levels of radioactive iodine, a material that accumulates in the thyroid.
How can the Japanese authorities minimise the cost to human health?
Professor Richard Wakeford, an expert in exposure to radiation, said provided the Japanese authorities acted quickly most of the general population should be spared significant health problems. He said in those circumstances the only people likely to be at risk of serious health effects were nuclear workers at the plant or emergency workers exposed to high levels of radiation.
He said the top priority would be to evacuate people from the area and to make sure they did not eat contaminated food. The biggest risk was that radioactive iodine could get into their system, raising the risk of thyroid cancer.
To counter that risk people could be given tablets containing stable iodine which would prevent the body absorbing the radioactive version.
| inspired by: CNN and BBC News Stories |
