This news comes as fears mount over the danger from earthquakes after media reports that a second plant in three months had been found to be sitting atop a faultline.

The review could lead to the permanent decommissioning of some nuclear plants in Japan, which prohibits their construction above active fault lines, and fuel a political storm over the future of nuclear power in the wake of the Fukushima disaster.

“We will hold hearings to get experts’ opinions on nuclear plants that were judged to have been based over no active faults in the past,” Trade and Industry Minister Yukio Edano.

“We are rechecking all plants.”

A review by Japan’s Nuclear and Industrial Safety Agency (NISA) of excavation data f or a reactor at the Shika station northwest of Tokyo indicates that an active fault line runs beneath it, Japanese media reported on Tuesday.

Shares in Hokuriku Electric Power Co and Japan’s other power utilities fell sharply on Monday, after a government panel called for breaking up their regional monopolies.

They were also hurt by the deepening uncertainty over the future of nuclear power, a little over two w eeks after the first restart of one of Japan’s reactors — which have steadily gone offline for routine maintenance — since the Fukushima disaster 16 months ago. Hokuriku Power fell 8,3% while Tokyo Electric Power Co, operator of the Fukushima plant, fell 11,5%.

Tokyo witnessed its biggest demonstration yet against nuclear power during a national holiday on Monday and the government has come under fire for its handling of public hearings on nuclear energy policy.

The media reports on the Shika plant faultline, citing regulatory reviews that NISA experts are considering at a meeting on Tuesday, come after NISA said in April it was concerned about an active fault under the Tsuruga nuclear plant not far from Shika and operated by unlisted Japan Atomic Power Co.

Hokuriku Electric said in a statement on Tuesday that it stood by its findings that the fault line below the 19-year-old Shika reactor is inactive.

Japan’s nuclear plants have been undergoing safety assessments after an earthquake and tsunami in March last year triggered three reactor meltdowns at the Fukushima Daiichi plant about 240 km (150 miles) north of Tokyo, the world’s worst nuclear disaster since Chernobyl in 1986.

The Fukushima disaster, which caused mass evacuations and contaminated a wide swathe of land, has brought reactor safety to the forefront in Japan.

The decision by Prime Minister Yoshihiko Noda last month to restart two reactors at the Ohi nuclear plant, on the same stretch of coastline as Shika and Tsuruga, has prompted regular street protests, including Monday’s march in central Tokyo that drew more than 100 000 demonstrators.