The UN's nuclear watchdog on Tuesday gave its seal of approval to Japan's reactor safety checks, but said utilities should beef up plans for managing disasters in the wake of the Fukushima meltdowns.

A delegation from the International Atomic Energy Agency (IAEA) is in the country at the government's invitation as officials look for ways to convince a deeply sceptical population that idled nuclear plants are safe to restart.

With just a handful of Japan's 54 reactors still operational, officials are nervously eyeing possible electricity shortfalls unless reactors are brought back online -- something that can only be done if local communities consent.

The government's Nuclear and Industrial Safety Agency (NISA) asked the IAEA to assess the stringency of the so-called stress tests to which all reactors are subjected before being given the green light to resume operations.

"The conclusion of the team is that NISA's instructions and review process for the comprehensive safety assessments are generally consistent with IAEA safety standards," the delegation said in a statement.

But the watchdog said further tests of the reactors should also look at how the utilities operating them would deal with a worst-case scenario.

"NISA should ensure that in the secondary assessment the provisions for mitigation of severe accidents should be addressed more comprehensively," the report said.

NISA should make sure companies "develop comprehensive accident management programmes ... in the area of severe accident management," it said.

The mission also urged Tokyo to engage with people living in the shadow of nuclear plants as it tries to convince them the technology is safe.

The stress tests were introduced as a way of determining how reactors would cope with the impact of large-scale natural disasters after meltdowns and explosions at Fukushima Daiichi caused by last March's earthquake and tsunami.

Radiation was scattered over a large area and made its way into the oceans, air and food chain in the weeks and months after the disaster, reversing the mood among Japan's once nuclear-friendly public.

"In any of these processes, the more information can be exchanged with the people in the local vicinity, the better," the delegation's team leader James Lyons told a news conference.

But he noted that Japan, not the IAEA, has to decide on whether to restart nuclear power plants in the country, saying: "That's not part of our decision making process."

The energy-hungry nation has virtually no natural resources of its own and relied on atomic power for around a third of its electricity before March 11.

Since the disaster the vast bulk of nuclear plants have been shut down as local authorities blocked their being restarted following routine safety checks or maintenance.

Japan has instead had to massively ramp up imports of fossil fuels and curb power useage as it tries to make up the shortfall in power generation.

More than 19,000 people died in the natural disaster, but the nuclear emergency -- the world's worst since Chernobyl a quarter of a century ago -- has not directly claimed any lives.

However, tens of thousands of people were forced from their homes around the plant as radiation levels rocketed, with many not knowing when -- or even if -- they will be allowed to return.