A Japanese power firm on Monday resumed construction of an atomic reactor stalled since the disaster at Fukushima, despite government plans to phase out nuclear power.

Electric Power Development, known as J-Power, said it had gone back to work on the plant in the country's north after getting the green light when the government announced its new energy policy aims last month.

The construction work in Oma, a town 650 kilometres (400 miles) north of Tokyo, is the first since a massive earthquake and tsunami sparked the disaster at Fukushima in March 2011 -- the worst such accident in a generation.

Economy, trade and industry minister Yukio Edano, who is charged with supervising the power industry, said the resumption had been a procedural matter and was a decision by the company.

But he added that the operator of the nuclear plant must still meet safety standards before power generation can begin there.

The firm made no announcement on when it expects work to be completed.

Last month, Prime Minister Yoshihiko Noda's government adopted a new energy policy that included the phasing out of nuclear power by 2040, in what was widely seen as bowing to public pressure after the Fukushima disaster.

The new policy calls for reactors more than 40 years old to be shut down, plans to build more nuclear reactors to be shelved and existing reactors only to be restarted if they pass standards issued by a new regulatory agency.

However the policy has been criticised as unclear, with several exceptions that could see nuclear power in use well past 2040. Partially-constructed reactors can be completed, for example.

Nuclear energy has become a hot-button issue in Japan before a general election expected this year. Protests calling for atomic power to be ditched have attracted tens of thousands of people.

Japan turned off its 50 reactors in the wake of the Fukushima disaster, with all but two of them still mothballed in the face of public opposition to their use.