Chief Cabinet Secretary Yukio Edano confirmed at a press conference Monday that a hydrogen blast occurred at the No.3 reactor of Fukushima No.1 nuclear power plant.

According to the Nuclear and Industrial Safety Agency, the explosion, which happened at 11:01 a.m. (0201 GMT), was similar to the one that hit the No. 1 reactor at the same plant Saturday.

The safety agency, meanwhile, urged the 600 residents within a 20-km radius of the troubled plant to stay indoors to avoid exposure to possible radioactive substances.

Nippon TV reported that the blast has caused some injuries.

The No. 3 reactor at the plant lost its ability to cool the reactor core early Sunday, becoming the sixth reactor that lost the function. And a hydrogen explosion is possible at the No. 3 reactor.

An official of the Japan Nuclear and Industrial Safety Agency said that the emergency cooling system of the No. 3 reactor is no longer functioning.

The 11:01 a.m. incident came after a hydrogen explosion hit the No. 1 reactor at the same plant Saturday, and prompted the Nuclear and Industrial Safety Agency to urge residents within a 20- kilometer radius to take shelter inside buildings.

It also followed a report by Tokyo Electric Power Co., the plant's operator, to the government earlier in the day that the radiation level at the plant had again exceeded the legal limit and pressure in the container of the No. 3 reactor had increased.

The Fukushima No. 1 nuclear plant has been shut down since a magnitude 9.0 quake struck northeastern and eastern Japan on Friday, but some of its reactors have lost their cooling functions, leading to brief rises in the radiation level over the weekend.

(Xinhua News Agency March 14, 2011)