Radiation levels jumped significantly minutes after a blast Tuesday at one of six reactors at a nuclear power plant in north-eastern Japan, the operating company said.
The Tokyo Electric Power Co (TEPCO) said after the 6:10 am (2110 GMT Monday) blast at reactor number 2 at the Fukushima plant, radiation levels rose to 965.5 microsievert per hour, well above the legal limit of 500 microsievert per hour, dpa reported.
At 8:31 am, radiation had exceeded 8,217 microsievert, more than eight times the allowed annual exposure level, the Kyodo News Agency reported, citing TEPCO.
TEPCO also admitted that a meltdown, a critical nuclear accident in which fuel rods melt and are destroyed, was possible, Kyodo said.
The cooling systems for the plant's reactors were damaged in Friday's magnitude-9 quake.