An explosion at a Japanese nuclear plant has exposed the scale of the disaster facing the country after a powerful earthquake and tsunami left more than 1,300 dead and many thousands missing.
Radiation leaked from an earthquake-crippled nuclear plant in Japan after a blast blew off the roof, and authorities prepared to distribute iodine to local people to protect them from exposure.
The government insisted radiation levels were low because although the explosion severely damaged the main building of the plant, it had not affected the reactor core container.
Japan's nuclear safety agency said the accident rated less serious than either the Three Mile Island or Chernobyl disasters.
An official of Japan's nuclear safety agency said the number of individuals exposed to radiation from the quake-hit Fukushima nuclear power plant could reach as high as 160.
Nine people had already shown possible exposure to radiation from the plant, based on information from tests by municipal authorities and other sources.
Kyodo news agency said more than 1,700 people were killed or missing as a result of the 8.9-magnitude quake, the biggest in Japan since records began in the 19th century.
Later it said 9,500 people in one town were unreachable, but gave no other details.
The blast raised fears of a meltdown at the power facility, 240km (150 miles) north of Tokyo, as officials scrambled to contain what could be the worst nuclear disaster since the Chernobyl explosion in 1986.
However, experts said Japan should not expect a repeat of Chernobyl. They said pictures of mist above the plant suggested only small amounts of radiation had been expelled as part of measures to ensure its stability, far from the radioactive clouds Chernobyl spewed out 25 years ago.
Japan's nuclear safety agency said it was rating the incident a 4 on the 1 to 7 International Nuclear and Radiological Event Scale (INES), less serious than 1979's Three Mile Island, which was rated a 5, and Chernobyl at 7.
The wind at the disabled plant was blowing from the south, which could affect residents north of the facility, Japan's national weather forecaster said, adding the direction may shift later so that it blows from the north-west towards the sea.
The direction of the wind is a key factor in judging possible damage on the environment from radiation.
Along the northeast coast, rescue workers searched through the rubble of destroyed buildings, cars and boats, looking for survivors in hardest-hit areas such as the city of Sendai, 300km (180 miles) northeast of Tokyo.
Dazed residents hoarded water and huddled in makeshift shelters in near-freezing temperatures. Aerial footage showed buildings and trains strewn over mudflats like children's toys.
Across the coastline, survivors clambered over nearly impassable roads. In Iwanuma, not far from Sendai, people spelled SOS out on the roof of a hospital surrounded by water, one of many desperate scenes.
The earthquake and tsunami, and now the radiation leak, present Japan's government with its biggest challenge in a generation.
The blast at the nuclear facility came as plant operator Tokyo Electric Power Co (TEPCO) was working desperately to reduce pressures in the core of the reactor.
The international community started to send disaster relief teams on Saturday to help Japan, with the United Nations sending a group to help coordinate work.
The earthquake was the fifth most powerful to hit the world in the past century. It surpassed the Great Kanto quake of 1 September, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.
Japan sits on the ‘Pacific Ring of Fire’ and Tokyo is in one of its most dangerous areas, where three continental plates are slowly grinding against each other, building up enormous seismic pressure.
The government has long warned of the likelihood that a devastating magnitude-eight quake will strike within the next 30 years in the Kanto plains, home to Tokyo's vast urban sprawl.
