Japanese officials are investigating the possibility of a second radioactive leak from a nuclear plant, following Monday's earthquake in central Japan.

Drums with low-level nuclear waste fell over during the tremors, and some of their lids were found open.

Water containing radioactive material is already known to have leaked from the plant into the sea, but officials say it will not harm the environment.

Monday's quake killed nine people and flattened hundreds of homes.

Thousands of people affected by the tremor - which was centred off the coast of Niigata - have crowded into evacuation centres.

Large parts of the coastal town of Kashiwazaki remain without power and water.

Rescue workers are looking for survivors in the rubble, while attempts are being made to restore severed utilities.

"The damage is more than we had imagined," said Kashiwazaki's Mayor, Hiroshi Aida, during a tour of the town.

"We want to restore the water supply as soon as possible so more people can return home."

Safety concerns

Kensuke Takeuchi, a spokesman at the Kashiwazaki Kariwa nuclear plant, confirmed that barrels of low-level nuclear waste had tipped over, but said he could not say whether there had been a leak.

"We're currently investigating the situation and plan to deal with it as smoothly as possible," the Associated Press news agency quoted him as saying.

The Kyodo news agency reported that about 100 drums had fallen over, and that this was discovered on Tuesday, a day after the quake.

There have long been concerns about the safety of Japan's nuclear power plants, which many fear are vulnerable in earthquakes.

Monday's 6.8-magnitude quake sparked a small fire at an electrical transformer in the Kashiwazaki plant, the world's largest in terms of power output capacity.

It was later announced that the tremors had also caused a leak of water containing radioactive material. Officials later said the water leak was harmless.

PHOTO CAPTION

Black smoke is seen spewing from an electricity transformer at Tokyo Electric Power Co.'s Kashiwazaki-Kariwa No.3 nuclear power generation unit in Kashiwazaki, northern Japan, July 16, 2007. (REUTERS)