Japan has said it will run "stress tests" on all its nuclear reactors in the wake of the Fukushima Daiichi atomic accident sparked by the March 11 earthquake and tsunami disaster.

The ongoing crisis, the world's worst atomic accident since Chernobyl 25 years ago, has ignited debate in Japan about the safety of nuclear power, which before the disaster accounted for one third of its electricity needs.

The centre-left government ordered a round of initial tests on the country's other atomic power plant after the disaster, and said on Wednesday the new stress tests aimed to reassure the public that the facilities are safe.

"The safety of nuclear power plants has been secured, but this is to gain a further sense of security among the people," Banri Kaieda, Japan's economy and industry minister, said.

He did not immediately give details of what the tests would entail or when they would start, saying only they would commence soon.

Triple disaster

Japan's nuclear crisis was sparked by a powerful 9.0 seabed quake, the country's biggest on record, that sent a massive tsunami barrelling into the northern Pacific coastline, shattering entire towns.

Amid a power blackout, the wave knocked out back-up generators, which disabled reactor cooling systems and led to meltdowns, explosions and continuing leakage of radiation into the air, soil and sea.

Utilities not directly affected by the seismic disaster have refrained from restarting reactors that were undergoing maintenance at the time, amid objections from local governments and a wave of anti-nuclear sentiment.

Only 19 of Japan's 54 reactors are now operating, with more due to shut down for regular checks soon, forcing companies and households to save power in the sweltering summer months.

In May, Naoto Kan, Japan's prime minister, told the operator of another quake and tsunami-prone plant, the ageing Hamaoka facility southwest of Tokyo, to shut down its reactors until it builds higher sea defences.

European fallout

In the wake of the Fukushima crisis, the European Union ordered stress tests for its 143 nuclear plants starting June 1, saying it would look at how they could withstand extreme and multiple disasters previously considered unthinkable.

The EU said the facilities would be checked for natural disasters such as quakes, floods and fires, as well as man-made disasters such as plane crashes and terrorist attacks, and combinations of such events.

Nuclear facilities are also to be tested for their resilience to extreme cold, extreme heat, snow, ice, storms, tornadoes, heavy rain and other extreme natural conditions.

The EU tests were to start with questionnaires to be checked by national regulators, followed by peer reviews among the 27 national authorities, of whom 14 have nuclear power and 13 do not.