Japanese Prime Minister Naoto Kan lost his cool when it emerged that he was kept in the dark for one hour about an explosion in the Fukushima No 1 nuclear plant.

Kan blasted the officials of the Tokyo Electric Power Company (TEPCO), which runs the plant, at a meeting on Tuesday, according to Kyodo News agency.

The TV reported an explosion. But nothing was said to the premier's office for about an hour ... What the hell is going on?, asked Kan, the report said.

Kyodo said a reporter overheard the prime minister while he was speaking with TEPCO officials.