Kashiwazaki city and Kariwa village - home to 100,000 people and otherwise known for their fine beaches - are no strangers to disaster.

On July 16, 2007 the area was hit by a strong earthquake, measuring 6.8 on the Richter scale, which killed 15 people.

The tremor, which struck 60 kilometres offshore in the Sea of Japan (East Sea), injured 2,346 people, mostly in Niigata prefecture, and damaged or destroyed more than 30,000 buildings.

Among the structures hit was the nuclear plant, one of Japan's oldest, where the first reactor started generating electricity in 1985.

Plant operator Tokyo Electric Power Co (TEPCO) said an electric transformer caught fire and more than 400 barrels with contaminated waste toppled over, with at least 40 spilling their contents.

The operator caused even greater concern when it said water from a spent fuel-rod pool leaked through drainage pipes into the ocean. Authorities immediately froze operations at the plant.

Since then TEPCO has reported nine fires inside the dormant facility, most recently last weekend.

Industry Minister Toshihiro Nikai chastised the operators, saying: 'Other countries have been paying attention to whether we'll be able to restart our country's biggest nuclear power plant.' Japan - located on the 'Pacific Ring of Fire,' where continental plates meet and create a string of volcanoes and seismic hot spots - records 20 per cent of the world's major earthquakes.

As an industrial powerhouse nation poor in energy resources, Japan also draws about 30 per cent of its total power from its 53 nuclear plants.

Since the 2007 quake hit the Kashiwazaki-Kariwa plant, TEPCO says it has upgraded it to withstand a tremor of seven on the Richter scale, a process which a government-appointed panel of 70 scientists has signed off on.

Nuclear and Industrial Safety Agency spokesman Minoru Ohkota told AFP: 'We assumed that there might be unknown risks, so we've added leeway to the quake-resistance standard to ensure the safety of the plant.' But Kobe University professor emeritus Katsuhiko Ishibashi argues that the benchmark should be raised to resist a 7.5-magnitude quake, citing evidence of a major seafloor faultline near the plant.

The government denies the existence of the faultline, acknowledging only a 36 kilometre-long crack in the seafloor, which Ishibashi calls 'a branched faultline of the main one'.

Professor Ishibashi described the review as 'illogical and unscientific and ignores residents' safety'.

At least three of Japan's 15 leading tectonics experts agree the larger fault exists, said Toyo University professor Mitsuhisa Watanabe.

'It's impossible to prove the existence of the (main) fault, but we see circumstantial evidence,' said Professor Watanabe.

'I'm not against nuclear power plants. But I say that the government's calculation of active faults is wrong,' he said.

'They should correct it, especially because it involves a nuclear plant.'