A Japanese utility on Friday said it started up a nuclear reactor, the fourth to come back online following a nationwide shutdown after the March 2011 tsunami disaster.

The government of Prime Minister Shinzo Abe and utility companies have been pushing to get reactors back in operation nearly five years after a huge earthquake and tsunami caused a disastrous meltdown at the Fukushima nuclear power plant in northeastern Japan.

The accident forced all of Japan's dozens of reactors offline for about two years in the face of public worries over the safety of nuclear technology and fears about radiation exposure.

But Abe, who came to power nearly two years after the 2011 disaster, has pushed the resumption of nuclear power as a vital part of the country's energy policy.

Kansai Electric Power resumed operations of its No. 4 reactor at the Takahama plant, 380 kilometres (236 miles) west of Tokyo, the Osaka-based company said on its website.

Earlier this month, the operator was forced to suspend part of the preparation process after some 34 litres (8.8 gallons) of cooling water containing radioactive substances leaked out from the reactor.

"But we resumed resumption work as we concluded that a bolt had not been tightened properly," a company spokesman said.

Last month, another reactor at Kansai Electric Power's Takahama plant was switched on, amid stiff opposition from local residents.

The region's Fukui District Court in December overturned an injunction preventing a restart of the two reactors which had been won by residents, who argued it was not proven to be safe despite a green light from the national Nuclear Regulation Authority.

Two reactors in the southern prefecture of Kagoshima, operated by Kyushu Electric Power, restarted in August and October of last year, ending the two-year hiatus in nuclear power generation.

Despite official assurances, many Japanese remain wary and thousands of former residents have refused to return to areas hit by the Fukushima meltdown over fears of radiation exposure.