Japan scrambled on Saturday to avert a disastrous meltdown at a nuclear plant damaged when a massive earthquake and tsunami struck the Northeast coast, killing at least 1,300 people.
Jiji news agency said there had been an explosion at the stricken 40-year-old Daichi 1 reactor and TV footage showed vapour rising from the plant, which lies 240 km (150 miles) north of Tokyo.
The country's nuclear safety agency could not confirm the reported incident, which 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.
"An unchecked rise in temperature could cause the core to essentially turn into a molten mass that could burn through the reactor vessel," political risk information service Stratfor said in a report. "This may lead to a release of an unchecked amount of radiation into the containment building that surrounds the reactor."
NHK television said the outer structure of the building that houses the reactor appeared to have blown off, which
could suggest the containment building had already been breached.
Earlier the operator released what it said was a tiny amount of radioactive steam to reduce the pressure and the danger was minimal because tens of thousands of people had already been evacuated from the vicinity.
Media reports estimate at least 1,300 people may have been killed by the 8.9 quake, the biggest since records began in Japan 140 years ago, and the 10-metre tsunami that swept ferociously inland after it struck.
Italy's National Institute of Geophysics and Volcanology said the earth's axis had shifted 25 cm as a result of the quake and the U.S. Geological Survey said the main island of Japan had actually shifted 2.4 metres.
Japanese officials and experts have been at pains to say that while there would be radiation leaks, they would be very small and have dismissed suggestions of a repeat of a Chernobyl-type disaster.
THOUSANDS FLEE
On Friday's tremor was so huge that thousands fled their homes from coastlines around the Pacific Rim, as far away as North and South America, fearful of a tsunami.
Most appeared to have been spared anything more serious than some high waves, unlike Japan's Northeast coastline which was hammered by the huge tsunami that turned houses and ships into floating debris as it surged into cities and villages, sweeping aside everything in its path.
"I thought I was going to die," said Watauga Fuji, a 38-year-old sales representative in Koriyama, Fukushima, North of Tokyo and close to the area worst hit by the quake.
"Our furniture and shelves had all fallen over and there were cracks in the apartment building, so we spent the whole night in the car. Now we're back home trying to clean."