Meltdown at reactors as 200,000 evacuated
Japan is in a race to prevent a nuclear and humanitarian disaster.
It faces a nuclear crisis on multiple fronts with two atomic reactors in partial meltdown and four others heating up as the failure of ageing plants forced the evacuation of about 200,000 people.
There is an exclusion zone of 20km around the 40-year-old Fukushima Daiichi nuclear complex where engineers battled to prevent three reactors overheating after the tsunami exposed flaws in the plant's cooling system.
The Japanese government insisted only a small amount of radioactive material had been released. Two other facilities in Tokai, 120km north of Tokyo, and Onagawa, north of Fukushima, were also subject to alerts.
Officials were helpless to prevent the core of reactor number one overheating at Fukushima, causing an explosion in the outer building.
A mass contamination screening programme was ordered for evacuees as questions were being asked about the future of Japan's flawed nuclear industry.
As rescuers struggled to reach tens of thousands of people left homeless by the tsunami, the government sent out an urgent international appeal for tents, blankets and other life-saving supplies to prevent the death toll rising beyond the current estimate of 10,000.
With night-time temperatures dropping below zero in some of the isolated towns and villages worst-affected by the disaster, charities warned that further lives could be lost if survivors were not given food and shelter quickly.
Last night, 590,000 people, many of whom have lost their homes, were living in temporary shelters, including those evacuated from the area around the Fukushima nuclear power plant.
Although the official death toll stood at 1,596, the true scale of the tragedy remained unclear, with tens of thousands of people still unaccounted for.
Seismologists upgraded the size of the "superquake" from 8.9-magnitude to 9.0, meaning it was twice as powerful as originally thought.
Japan's Prime Minister Naoto Kan said the country was experiencing its worst crisis since World War Two as it struggled to cope with the aftermath of the tsunami on several fronts.
As well as the overwhelming scale of the relief effort along a 2,100km-stretch of coastline, and the battle to avert a nuclear meltdown at the Fukushima plant, there were fears that Japan could be tipped back into recession, with cost of the disaster expected to run into tens of billions of euro.
The reactors themselves did not suffer any substantial structural damage in the initial quake. But what the engineers had not anticipated was the effect the resulting tsunami would have on vital power supplies at nuclear power plants positioned along the Pacific coastline.
Travelling at 100kmh, the 9m wave crippled back-up diesel generators, which were supposed to kick in and maintain the cooling systems in the event of a quake.
Fukushima's number one reactor was due to be decommissioned last month, but had its operating licence extended for another 10 years due to the demand for electricity. Officials insisted that the explosion had not breached the core so had not resulted in a major release of radioactive material.
But with the plant's other two reactors also struggling with rising temperatures, the Japanese government was forced to concede that further explosions and leaks were possible.
Officials flooded the reactors with seawater in a last ditch attempt to prevent overheating. This will render the reactors unusable in the future.
The crisis at the plant -- where the outer shell of the building that housed reactor number one exploded on Saturday -- was rated as a four out of seven on the International Nuclear and Radiological Event Scale, compared with a five for Three Mile Island and seven for Chernobyl.
The government admitted there was a risk of a second explosion at the site, but insisted there was no major health risk, despite 160 people being exposed to radiation at the plant over the weekend, of whom 22 suffered contamination.
A state of emergency was also declared at the Onagawa nuclear power plant because of high radiological readings, though officials insisted the cooling system was intact and the readings had been caused by a cloud of radiation spreading from Fukushima.
There were also reports last night of a problem with the cooling system at the Tokai number two reactor.
The most pressing problem facing the government was the need to avert the humanitarian crisis, as 1.4 million people remained without water. Thousands more were thought to be sleeping in makeshift shelters in areas that were still cut off.
The final death toll from Friday's events is unlikely to be known for weeks, but police in the Miyagi prefecture, which includes the devastated port of Sendai, said 10,000 lives were likely to have been lost there alone.
As rescue teams from more than 70 countries helped sift through the rubble of collapsed buildings and tried to reach those still stranded, there were warnings that the country was in danger of more earthquakes.
Japan's meteorological agency said there was a 70pc chance of a magnitude-7.0 tremor hitting the region in the next three days -- significantly smaller than Friday's earthquake but bigger than any of the scores of aftershocks over the weekend.
An estimated 2.6 million homes were without electricity and Mr Kan approved a plan to ration power to three million homes around Tokyo by imposing a "rolling blackout".