TOKYO (BLOOMBERG) - Japan restarted the first nuclear reactor in more than three years, a long-awaited step forward for the nation's utilities that are struggling to gain local support and fulfill onerous regulatory requirements.

Kansai Electric Power on Wednesday (June 23) morning resumed operations of its Mihama No. 3 reactor, which has been offline for more than a decade, according to a faxed statement.

Still, the unit will likely have to temporarily shut down again later this year as it will not be able to finish required upgrades ahead of an October deadline.

The restart is a shot in the arm for Prime Minister Yoshihide Suga's government, which supports resuming the reactors despite a large swath of the public that harbours deep concerns over safety after the 2011 Fukushima earthquake and tsunami.

Utilities have been unable to quickly resume units due to a litany of required safety upgrades, local opposition and court challenges.

Only 10 of Japan's 33 operable nuclear units have resumed operations under the regulatory regime created in the wake of the Fukushima nuclear disaster.

The nation will need nearly all of those units online to meet its 2030 pollution reduction goals.

Mihama's restart will also help ease a power supply crunch expected this summer. The government warned last month that hot weather and plant outages will curb the power reserves.

Mihama No. 3 is the first unit over 40 years old to resume operations under the post-Fukushima regulatory framework, which has made it a lightning rod for anti-nuclear opponents.

A citizens group has filed a lawsuit seeking to halt operations of the reactor on the grounds that its old age makes it unsafe, according to broadcaster NHK.

While Kansai Electric has received local approval to restart two more units over 40 years old, it is unclear when they will finish necessary upgrades.

Separately, Japan's Nuclear Regulation Authority said Wednesday that Chugoku Electric Power's Shimane No. 2 nuclear reactor passed a safety assessment, one of the biggest hurdles before resuming operations. Chugoku applied for the regulatory review in 2013.

Shimane is the 17th reactor endorsed by Japan's nuclear watchdog, and the latest approval since 2019.

Nuclear power advocates have complained that the regulatory review is too time consuming and slows the restart of reactors.

If the unit completes safety upgrades and receives local approval, it can restart as soon as the fiscal year ending March 2023, the Nikkei reported.