The blast and fire have turned the nuclear plants "critical", the country's chief spokesman announced as the melting reactors spewed large amounts of radioactive materials triggering fear of widespread contamination.
Kan in his address to the nation at 11 am local time warned that the radiation had already spread from the crippled reactors and there was "a very high risk of further leakage" as the French embassy here said that low-level radioactive could reach the capital Tokyo within hours.
The Japanese Prime Minister asked an estimated 140,000 people living within 30 kms of the facility north of capital to remain indoors and to conserve power as threat loomed large of Japan''s crisis turning into a Chernobyl-like disaster.
Kyodo quoting nuclear experts said radiation equivalent to 400 times the level to which people can be exposed in one year was detected near the Fukushima No 3 reactor.
Residents within a 20-km radius of the plant have already been ordered to vacate the area following Saturday''s hydrogen blast at the plant's No 1 reactor.
The Japanese news agency quoting Chief Cabinet Secretary Yukio Edano said the high radiation level detected at 10:22 am local time after the explosions at the No 2 and No 4 reactors "would certainly have negative effects on the human body".