Radiation levels at the quake-damaged Fukushima nuclear plant in Japan, which has been hit by a second explosion, are "normal", the UN atomic watchdog IAEA said today.

"Radiation dose rate measurements observed at four locations around the plant's perimeter over a 16-hour period on March 13 were all normal," the International Atomic Energy Agency said in a statement.

An explosion shook the Fukushima nuclear power plant today, injuring six people, but officials said the reactor container was not breached and there was no major rise in radiation.

The blast was caused by a build-up of hydrogen in the building around the No 3 reactor at the Fukushima Number One plant, said chief government spokesman Yukio Edano.

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