At least eleven people were injured in a second explosion at the Fukushima nuclear plant in north-eastern Japan on Monday, NHK TV said.
The build-up of hydrogen caused reactor no. 3 to explode at around 02:00 GMT but the government's top spokesman, Yukio Edano, said its core was still intact. He said there was a "low possibility" of a rise in radiation levels near the damaged plant.
A blast occurred in the plant's reactor no. 1 on Saturday.
The plant's operator, Tokyo Electric Power Co., told the TV station that the cooling system at reactor no. 2 has failed.
Seawater is still being pumped into the reactors in an attempt to cool them, officials say.
The plant's cooling system was knocked out by a powerful earthquake and tsunami on Friday that is believed to have left at least 10,000 people dead in north-east Japan.
Officials in Russia's Far East say the new blast has not caused a significant rise in radiation levels in the region.
MOSCOW, March 14 (RIA Novosti)