An explosion blew the roof off an unstable reactor north of Tokyo on Saturday, Japanese media said, raising fears of a disastrous meltdown at a nuclear plant damaged in the massive earthquake that hit Japan.
Explosion at Japan's quake-hit nuclear plant
The 8.9-magnitude earthquake the strongest ever recorded in Japan sent a 10-metre tsunami ripping through towns and cities across the northeast coast. Japanese media estimate that at least 1,300 people were killed.
Jiji news agency said there had been an explosion at the stricken 40-year-old Daichi 1 reactor and TV footage showed vapor rising from the plant, which lies 240 km (150 miles) north of Tokyo.
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.
"An unchecked rise in temperature could cause the core to essentially turn into a molten mass that could burn through the reactor vessel," 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 and Jiji 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.