The governor of Japan's Niigata prefecture easily defeated his anti-nuclear opponent in an election on Sunday, public broadcaster NHK said, a result that could embolden members of the ruling party who are pushing for the country's largely idled nuclear energy plants to be revived.

Hideyo Hanazumi, who was backed by Prime Minister Fumio Kishida's ruling Liberal Democratic Party (LDP), beat local businesswoman and longtime activist against nuclear energy, Naomi Katagiri by a large margin, NHK said, citing exit polls.

It did not give exact figures, but Hanazumi also claimed victory in a speech to supporters.

The vote in Niigata, home to the world's largest nuclear power plant, was closely watched by LDP heavyweights in Tokyo as a gauge of voter readiness to re-embrace nuclear power.

Dozens of Japan's reactors were idled in the aftermath of the 2011 Fukushima nuclear disaster, including the Kashiwazaki-Kariwa plant in Niigata. Although many Japanese are wary of nuclear power, the Ukraine crisis and a tumbling yen have led to a surge in energy costs, hitting households.

In the last gubernatorial election in Niigata four years ago, nuclear power was the main issue. This time it ranked fifth for voters, according to a recent survey by the Niigata Nippo newspaper, having been eclipsed by economic concerns.

Hanazumi had been expected to win easily this time. During his campaign he tried to steer clear of the nuclear issue and when asked about it, echoed the government line that safety is the priority.

Kishida said on Friday Japan will take concrete steps to restart idled nuclear power plants with a priority given to safety, to stabilise energy prices and supply.

Only 10 nuclear reactors are operational in Japan, compared with 54 before the Fukushima disaster. The government aims to raise the nuclear power contribution in its energy mix up to 22% by 2030, from 6% in 2019.