Japan's trade ministry ordered nuclear power plant operators to take immediate steps to improve emergency preparedness and will review energy policies to promote renewable sources and ease power shortages as it grapples with a nuclear safety crisis.

The ministry said on Wednesday that nuclear plants would be required by mid-April to deploy back-up mobile power generators and fire trucks able to pump water, while beefing up training programmes and manuals, aiming to avoid a repeat of the crisis at the Fukushima nuclear plant.

It will also look at longer-term solutions such as requiring higher sea walls at nuclear stations and will review its energy policy to encourage renewables, although it reiterated that nuclear power was expected to retain an important role.

"As Prime Minister (Naoto) Kan has said in parliamentary debates, I think we should also put emphasis on renewable energy sources, such as solar power," Trade Minister Banri Kaieda told a news conference.

"We should discuss our energy policy as a whole."

The crippled Fukushima complex in northeastern Japan continues leaking radiation more than two weeks after it was battered by a magnitude 9.0 earthquake and a 14-metre (46-foot) tsunami.

The government and the plant's operator, Tokyo Electric Power Co, have conceded there is no end in sight to the world's worst nuclear crisis since the Chernobyl accident a quarter of a century ago.

IMMEDIATE STEPS

The immediate safety measures ordered by the ministry are intended to prevent a tsunami from knocking out power, and especially cooling systems, at nuclear reactors and pools of spent fuel rods, which was the main cause of the crises at four Fukushima Daiichi reactors.

The plants would be allowed to continue operations during the implementation of the safety measures, which must be verified by the government by end-April, in order to ensure sufficient power supplies.

"These are the minimum steps we can think of right now that should be done immediately," Kaieda said.

Japan's regional utilities have already announced plans to address safety concerns.

Central Japan's Chubu Electric Power Co said last week it would build a 12-metre tsunami wall over the next few years to protect its Hamaoka plant, located in a coastal region where the government has predicted a high probability of a major earthquake within the next three decades.

Kansai Electric Power Co, which serves Japan's second-largest metropolis in Osaka, said it would spend 50 billion to 100 billion yen ($620 million-$1.23 billion) on improving safety for its nuclear plants.

Nearly 90 percent of Japan's 54 reactors have yet to comply with upgraded 2006 safety guidelines for protection from a massive tsunami.

Kaieda said nuclear power, which accounts for 30 percent of Japan's electricity output, was an important part of its energy portfolio, and running reactors in the undamaged west was essential to secure power for overall industrial output.

The Tokyo area has been hit by rolling power blackouts since the quake took out more than 20 percent of Tokyo Electric's generating capacity, including the Fukushima complex.

Fears are mounting that wider power outages in the peak demand months of summer could severely harm Japan's economy.

Incompatible power frequencies in eastern and western Japan make it impossible for Tokyo and the battered northeast to tap power from the west, except through special linkage facilities that so far can only provide a modest 1,000 megawatts.

"We're studying measures now, but we'd like to have more power being provided to the east from the west," Kaieda said.

Tokyo Electric, which on Wednesday said it would scrap the Fukushima plant's four troubled reactors, could face a shortfall of nearly 10,000 MW in the summer.