The move to shutdown Hamaoka, seen at high risk to forecasts of a powerful earthquake in coming decades, follows pressure on the government to review Japan's nuclear energy policy after a March 11 quake and tsunami crippled another plant, triggering the world's worst nuclear accident in 25 years.

Kan, who has been under fire for his response to the crisis at Tokyo Electric Power Co's (TEPCO) Fukushima Daiichi plant in northeast Japan, said the government would try to prevent the halt of the Hamaoka reactors from causing power supply problems.

Companies in eastern and northeast Japan served by TEPCO and another quake-affected utility have already been asked to curb electricity usage this summer when demand peaks. The shutdown at Hamaoka raises the risk of power disruptions in the Chubu region, home to Toyota Motor Corp and other major manufacturers.

The Hamaoka decision signals a likely shift in Japan's energy policy, with the government now rethinking its target of boosting the country's reliance on nuclear to 50 percent of its power needs by 2030, up from 30 percent before the quake.

The 3,617 megawatt Hamaoka plant accounts for about 7 percent of Japan's combined nuclear power generating capacity. It is located about 200 kilometres (120 miles) southwest of Tokyo and sits near an active earthquake zone.

Chubu Electric's President Akihisa Mizuno said in a statement that the firm will "promptly consider" the request. Kyodo news agency, citing a Chubu source, reported that the company would comply with the government's decision.