Meltdown fears after explosion at Japan nuclear station

An explosion shattered a building housing a nuclear reactor today amid fears of a meltdown, while across wide swaths of north-eastern Japan officials searched for thousands of people missing more than a day after a devastating earthquake and tsunami.

The confirmed death toll from yesterday's twin disasters was 574, but the government's chief spokesman said it could exceed 1,000.

Devastation stretched hundreds of miles along the coast, where thousands of hungry survivors huddled in darkened emergency centres cut off from rescuers and aid.

The scale of destruction was not yet known, but there were grim signs that the death toll could soar. One report said four whole trains had disappeared and had still not been located.

Others said 9,500 people in one coastal town were unaccounted for and that at least 200 bodies had washed ashore elsewhere.

Atsushi Ito, an official in Miyagi prefecture, among the worst hit states, could not confirm those figures, noting that with so little access to the area, thousands of people in scores of towns could not be contacted or accounted for.

"Our estimates based on reported cases alone suggest that more than 1,000 people have lost their lives in the disaster," said Chief Cabinet Secretary Yukio Edano.

"Unfortunately, the actual damage could far exceed that number considering the difficulty assessing the full extent of damage."

Among the most worrying developments was the possible meltdown of a nuclear reactor near the quake's epicentre. Edano said an explosion caused by vented hydrogen gas destroyed the exterior walls of the building where the reactor is, but not the actual metal housing enveloping the reactor.

Edano said the radiation around the Fukushima Dai-ichi plant had not risen after the blast, but had in fact decreased, though he did not say why that was so.

Still, virtually any increase in ambient radiation can raise long-term cancer rates, and authorities were planning to distribute iodine, which helps protect against thyroid cancer.

Authorities have also evacuated people from a 12-mile radius around the reactor.

The explosion was caused by hydrogen interacting with oxygen outside the reactor. The hydrogen was formed when the superheated fuel rods came in contact with water being poured over it to prevent a meltdown.

Officials have said that radiation levels were elevated before the blast: At one point, the plant was releasing each hour the amount of radiation a person normally absorbs from the environment each year.

The explosion was preceded by puff of white smoke that gathered intensity until it became a huge cloud enveloping the entire facility, located in Fukushima, 20 miles from Iwaki. After the explosion, the walls of the building crumbled, leaving only a skeletal metal frame.

Tokyo Power Electric Co, the utility that runs the Fukushima Dai-ichi plant, said four workers suffered fractures and bruises and were being treated at a hospital.

The trouble began at the plant's Unit 1 after the massive 8.9-magnitude earthquake and the tsunami it spawned knocked out power there, depriving it of its cooling system.

Power was knocked out by the quake in large areas of Japan, which has requested increased energy supplies from Russia, Russia's RIA Novosti agency reported.

The concerns about a radiation leak at the nuclear power plant overshadowed the massive tragedy laid out along a 1,300-mile stretch of the coastline where scores of villages, towns and cities were battered by the tsunami, packing 23ft high waves.

It swept inland about six miles in some areas, swallowing boats, homes, cars, trees and everything else.

"The tsunami was unbelievably fast," said Koichi Takairin, a 34-year-old truck driver who was inside his sturdy four-ton rig when the wave hit the port town of Sendai.

"Smaller cars were being swept around me," he said. "All I could do was sit in my truck."

His rig ruined, he joined the steady flow of survivors who walked along the road away from the sea and back into the city today.

Smashed cars and small planes were jumbled up against buildings near the local airport, several miles from the shore. Felled trees and wooden debris lay everywhere as rescue workers coasted on boats through murky waters around flooded structures, nosing their way through a sea of debris.

Firefighters have yet to contain a large blaze at the Cosmo Oil refinery in the city of Ichihara.

According to official figures, 586 people are missing and 1,105 injured.

Prime Minister Naoto Kan said 50,000 troops joined rescue and recovery efforts, aided by boats and helicopters. Dozens of countries also offered help.

President Barack Obama pledged US assistance following what he called a potentially "catastrophic" disaster. He said one US aircraft carrier was already in Japan and a second was on its way.

More than 215,000 people were living in 1,350 temporary shelters in five prefectures, the national police agency said.

Since the quake, more than one million households have not had water, mostly concentrated in north-east. Some four million buildings were without power.

About 24% of electricity in Japan is produced by 55 nuclear power units in 17 plants and some were in trouble after the quake.

Japan declared states of emergency at two power plants after their units lost cooling ability.