A Japanese nuclear power plant has exploded, a day after a massive earthquake damaged the facility's cooling system. Residents have been warned to stay indoors.
Japanese media said an explosion blew the roof off the reactor, raising fears of a disastrous meltdown at the earthquake-struck Fukushima nuclear power plant.
Officials say hundreds have been injured and hundreds more are missing after yesterday's magnitude 8.9 quake triggered a tsunami up to 10-metres high, devastating the country's northeastern coast. It is feared more than 1300 people are dead.
Are you a Kiwi in Japan who experienced the earthquake or tsunami? Click here to contact the Stuff newsroom.
Four people were injured in the explosion that occurred at the No. 1 reactor, Kyodo News reported, and followed large tremors.
Nuclear authorities had earlier warned that the Fukushima No 1 plant, located about 250km northeast of Tokyo, an urban area of 30 million people, "may be experiencing a nuclear meltdown".
The plant's cooling system was damaged in the quake that hit on Friday, leaving the government scrambling to fix the problem and evacuate more than 45,000 residents within a 10km radius.
Public broadcaster NHK reported that a blast had been heard at about 3:30pm (local time) and showed delayed footage of smoke billowing from the site, also reporting that the reactor building had been destroyed.
TV channels warned nearby residents to stay indoors, turn off air-conditioners and not to drink tap water. People going outside were also told to aviod exposing their skin and to cover their faces with masks and wet towels.
The UN nuclear watchdog said it was urgently seeking information from the country's authorities following the reports.
"We are aware of the media reports and we are urgently seeking further information," the IAEA official told Reuters.
The blast came as plant operator Tokyo Electric Power Co (Tepco) worked desperately to reduce pressures in the core of the reactor that, if not contained, could lead to a release of radiation into the atmosphere.
Nuclear expert Mark Hibbs of the Carnegie Endowment for International Peace said an explosion would be a "physical shock" to the plant that could increase the danger of a breach of the containment and of radioactivy getting out.
"We don't have any information from inside the plant. That is the problem in this case," he said.
"If it melts down the probability that there would be a breach or that radiation would get outside of the plant because of weakness of the structure of the plant ... is much greater," Hibbs said.
Meanwhile Japan is pushing 50,000 rescue staff into quake and tsunami-devastated areas as officials warn they expect the death toll to "rise greatly".
The tsunami today reached Pacific nations, with at least five people swept out to sea and docks ripped from their moors in California. However, there was limited damage elsewhere.
Japan mobilised 50,000 military and other rescue personnel Saturday, as Chief Cabinet Secretary Yukio Edano warned the number of dead would "rise greatly''.
The United States, with almost 50,000 troops stationed in Japan, sent aircraft carriers to waters off the disaster zone as the relief effort gathered pace.
On the east coast of Japan's main island, Honshu, where at least 3,600 houses were destroyed, there were some hope as army helicopters airlifted people off the roof of an elementary school in Watari, Miyagi prefecture.
Miraculously, naval and coastguard choppers rescued 81 people from a ship that had been dragged out to sea by the tsunami.
Earlier operators at the Fukushima Daiichi plant's Unit 1 scrambled to take down heat and pressure inside the reactor after quake and tsunami that followed cut off electricity to the site and disabled emergency generators, knocking out the main cooling system.
Some 3000 people within three kilometres of the plant had already been urged to leave their homes, but the evacuation zone was more than tripled to 10 kilometres after authorities detected eight times the normal radiation levels outside the facility and 1,000 times normal inside Unit 1's control room.
Japan declared states of emergency today for five nuclear reactors at two power plants after the units lost cooling ability.
The International Atomic Energy Agency said in a statement earlier that diesel generators that normally would have kept cooling systems running at Fukushima Daiichi had been disabled by tsunami flooding.
A pregnant New Zealander living nearby earlier said she feared one of the plants would explode.
Jayne Nakata - Jayne Lark until she married a Japanese man - said one of the plants was about 50km from her home.
"If there was a large explosion we would be affected here,'' she said today.
Radiation levels inside the plant had increased 1000 times above the norm, although authorities said levels outside the facility's gates were only eight times above normal, which meant there was "no immediate health hazard''.
While some radiation leakage could be expected, Naoto Sekimura, a professor at the University of Tokyo, said a major radioactive disaster was not likely.
''Even in the worst-case scenario, that would mean some radioactive leakage and equipment damage, but not an explosion. If venting is done carefully, there will be little leakage. Certainly not beyond the 3km radius,'' he said.
The unfolding disaster prompted offers of search and rescue help from 45 countries, including New Zealand.
Prime Minister John Key said 48 New Zealand search and rescue staff would be on the ground in Japan by the end of Sunday.
China said rescuers were ready to help with quake relief while President Barack Obama told Japanese Prime Minister Naoto Kan the US would assist in any way.
Japanese politicians pushed for an emergency budget to fund relief efforts after Prime Minister Naoto 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 1300, most of whom appeared to have drowned by churning waters after the mid-afternoon earthquake.
FIRES ACROSS THE COAST
The quake sparked at least 80 fires in cities and towns along the coast, Kyodo said.
Power plants and oil refineries were shut down and one refinery was ablaze. Television footage showed an intense fire in the waterfront area near Sendai.
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.
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 the worst fears in the Americas were not realised.
BIGGEST OF ALL
The quake surpasses the Great Kanto quake of September 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.
- Reuters, AP and NZPA
Video sourced by: Marc Bailey
What is your unhealthy vice?Related story: We drink too much, smoke too much . . .
Look out your window and what do you see?
Romance, defiance and swagger
A roundup of the latest products from Norton
Two Jo Nesbo novels in quick succession: what a treat
Have fun, no running and no pictures
Mud in all of its glory
Follow the adventures of Janelle King who is working in Kenya