A small fire broke out today at a partly constructed nuclear power station in northern Japan, the third blaze at the plant this month. It comes a week after an earthquake caused a radioactive spillage at another atomic plant.

The operator, Hokkaido Electric Power (Hepco), said there was no danger of a radiation leak and there were no injuries during the incident at the Tomari plant.

Two other reactors at Tomari were operating normally, it said.

The Kyodo news agency said investigators found damage to electrical wiring and suspected foul play, but the operator was unavailable to comment.

The fire came eight days after an earthquake caused radiation leaks at the Kashiwazaki-Kariwa plant - which generates the most electricity of nuclear power stations worldwide.

International inspectors were due to visit the Kashiwazaki plant in the aftermath of the quake, in which 400 drums of low-level radioactive waste fell over, with about 40 losing their lids and spilling their contents.

The spillage was one of more than 50 malfunctions at the plant in the immediate aftermath of the quake. The operator, Tokyo Electric Power (Tepco), was criticised for failing to deal with the blaze and for initially under-reporting the scale of the radioactive leaks.

The Kashiwazaki plant has been closed indefinitely and Japan's 54 other nuclear power stations have been ordered to carry out emergency safety checks.

The Tomari plant has had problems before. In 2003, Hepco temporarily shut a reactor there after a leak in a coolant tank. And in 1995, four workers were badly burned when a radioactive waste tank caught fire.

Hepco said no radiation had leaked outside the compound in any of the cases.