Japan's Nuclear and Industrial Safety Agency said Tuesday that an explosion was heard at the No. 2 reactor of Fukushima No.1 nuclear power plant at 6:10 a.m. Tuesday (2110 GMT).
The suppression pool of the reactor might have been damaged at No. 2 reactor, said the safety agency.
A rise in radiation was monitored near the nuclear plant shortly after the blast, said the agency. The radiation fell to 882 micro sievert after briefly rising as high as 965.5 micro sievert, topping the legal limit of 500.
But the agency said that the radiation will not immediately affect people's health at the levels of above figures.
Tokyo Electric Power Co. (TEPCO), owner and operator of the Fukushima nuclear plants, said it is evacuating some workers from the plant, but those who is working to cool the reactor will remain there.
Prime Minister Naoto Kan said earlier Tuesday that the government and TEPCO will set up an integrated headquarters, headed by the premier, to address issues at the Fukushima No. 1 plant.
(Xinhua News Agency March 15, 2011)