The United Nations says up to 590,000 people have been forced to leave their homes in Japan over the last three days following the devastating earthquake and tsunami.
About 380,000 people have been left the tsunami and earthquake affected areas and are being sheltered in 2,050 evacuation centres.
At the same time there is growing anxiety about the reactors in a number of nuclear power stations.
According to the International Atomic Energy Agency, authorities have told another 210,000 people living within a 20km radius around the Fukushima plant to leave their homes.
The death toll is expected to exceed 10,000 from the quake and tsunami.
The world's third-largest economy is struggling to respond to a disaster of epic proportions, with more than 1m without water or power and whole towns wiped off the map.
‘The earthquake, tsunami and the nuclear incident have been the biggest crisis Japan has encountered in the 65 years since the end of World War II,’ Prime Minister Naoto Kan told a news conference.
‘We're under scrutiny on whether we, the Japanese people, can overcome this crisis.’
Nuclear emergency battle
Japan is battling a meltdown of two earthquake hit nuclear reactors.
An explosion at the ageing Fukushima No. 1 atomic plant blew apart the building housing one of its reactors yesterday.
The No. 1 reactor, where the roof blew off, is 40 years old and was originally scheduled to go out of commission in February but had its operating licence extended another 10 years.
Officials are working desperately to stop fuel rods in the damaged reactors from overheating, which could in turn melt the container that houses the core, or even explode, releasing radioactive material into the wind.
The cooling system pump has stopped at the Tokai No.2 nuclear power plant (Kyodo) in Japan's Ibaraki prefecture.
The government said a building housing a second reactor at the same complex was at risk of exploding. The complex is 240km north of Tokyo.
The number three reactor is also facing the risk of an explosion.
Seawater is being poured into a third reactor to release a build-up of pressure.
The shutdown of reactors across the zone will force rolling power outages nationwide and citizens have been urged to conserve energy.
Nuclear plant operator Tokyo Electric Power (TEPCO) has said that radiation levels around the Fukushima Daiichi plant had risen above the safety limit but that it did not mean an ‘immediate threat’ to human health.
A UN nuclear agency has said that excessive levels of radiation at a second Japanese nuclear facility after Friday's earthquake have led authorities to report a state of emergency there north of the town of Sendai.
But Japan's nuclear safety agency has said that there was no problem with the cooling process at Tohoku Electric Power Co's Onagawa nuclear power plant and that a rise in radiation levels there was due to radiation leakage at another plant in a neighbouring prefecture.
Malcolm Crick, Secretary of the UN Scientific Committee on the Effects of Atomic Radiation has said that health risks from Japan's quake-hit nuclear power reactors seem fairly low and winds are likely to carry any contamination out to the Pacific without threatening other nations.
A Japanese official has said there were 190 people within a 10km radius of the nuclear plant when radiation levels rose and 22 people have been confirmed to have suffered contamination.
Workers in protective clothing were scanning people arriving at evacuation centres for radioactive exposure.
Officials ordered the evacuation of a 20kms (12-mile) radius zone around the plant and 10kms (6 miles) around another nuclear facility close by.
Around 140,000 people had left the area, while authorities prepared to distribute iodine to protect people from radioactive exposure.
The wind over the plant would continue blowing from the south, which could affect residents north of the facility, an official at Japan's Meteorological Agency said.
Growing humanitarian crisis
The country faced a growing humanitarian crisis with millions of people without water, electricity, homes or heat.
Two days after entire neighbourhoods were submerged by waves that swallowed an estimated 5,000 homes, Rikuzentakata is one of many towns and cities facing both a fast-rising death toll and dwindling supplies of food, fuel and water.
Kyodo said about 300,000 people were evacuated nationwide, many seeking refuge in shelters, wrapped in blankets, some clutching each other sobbing.
It said 5.5m people were without power, while 20,800 buildings had been destroyed or damaged. Four trains were unaccounted for after the tsunami.
Tens of thousands of people had taken shelter in schools and stadiums to escape near-freezing temperatures.
Many expect the death toll to go higher.
Japan's Meteorological Agency's director of earthquake prediction has said that there is a 70% chance of a 7-magnitude aftershock within the next three days -- a shake that could destroy buildings and trigger more tsunamis.
The Department of Foreign Affairs says it has now accounted for all Irish citizens in Japan and all are described as 'safe and well' .
President Mary McAleese has said that 'on behalf of the people of Ireland and on my own behalf, I wish to convey
to you and the people of Japan deepest sympathy on the tragic loss of so
many lives in Friday's earthquake and tsunami which hit northern Japan.
Mary McAleese said 'I know that the task of tending to the injured and reconstructing what has been lost will be enormously challenging and difficult for your country.'
She continued, 'as a friend of Japan, Ireland is steadfast in its solidarity with you and your people at this most difficult time.'
The Minister for Foreign Affairs Eamon Gilmore has said that the Government will be offering support to the Red Cross effort to Japan.
Meanwhile, France has recommended that its citizens leave the Tokyo region, citing the risk of further earthquakes and uncertainty about the situation at its damaged nuclear plants.
'It seems reasonable to advise those who do not have a particular reason to stay in the Tokyo region to leave the Kanto (Tokyo) region for a few days,' a statement on the French embassy website in Japan said.
'We strongly advise our nationals not to travel to Japan and we strongly recommend delaying any voyage planned,' it added.
Pope Benedict XVI has hailed the 'courageous' Japanese people and called for prayers for the victims.