Japan began switching off its last operating nuclear reactor on Sunday for inspection, and no date has been scheduled for a restart amid strong public hostility toward atomic power.

The move leaves the world's third-largest economy without atomic energy for the second time since the Fukushima nuclear crisis erupted in March 2011.

Nuclear power supplied about one-third of the resource-poor nation's electricity before a tsunami knocked out cooling systems and sparked meltdowns at Fukushima, causing tens of thousands to flee their homes.

Prime Minister Shinzo Abe has openly supported a return to the widespread use of atomic energy, but the public remains largely opposed on safety grounds.

Kansai Electric Power on Sunday started to gradually take offline the No 4 reactor at its Oi nuclear plant in western Fukui prefecture.

"The work started at 4:40 pm," a company spokesman said on Sunday. "The reactor will come to a complete stop early tomorrow."

Japan was without any nuclear energy in May 2012, when all of the country's 50 commercial reactors stopped for checkups after the Fukushima disaster.

Utilities were immediately unable to restart them due to public opposition.

It was the first time in more than four decades that Japan had been without nuclear power.

Government officials and utilities voiced concern at the time that Japan could face major blackouts without nuclear power, particularly in the western region, which relied heavily on nuclear energy.

Their fears proved unfounded, but the government gave Kansai Electric approval to restart No 3 and No 4 reactors at the Oi plant last year, arguing that nuclear energy was necessary to meet increased electricity demand during the winter.

The reactors were reactivated in July 2012 and resumed full commercial operation the following month, but the No 3 reactor was shut down this month for a scheduled inspection. The nation's other reactors have remained idle.

Utilities have submitted applications this summer to restart their reactors with the Nuclear Regulation Authority, which has significantly upgraded safety standards since the Fukushima crisis.

The central government and utilities will seek the consent of local governments and communities hosting nuclear plants before any future restarts.

The No 3 reactor at the Ikata nuclear plant in Ehime prefecture in the southwestern Shikoku region may come back online early next year, Sankei Shimbun reported.

Asahi Shimbun, meanwhile, reported the reactor at Ikata might resume operation in "the coming winter".

Anti-nuclear campaigner Greenpeace Japan said the country must seize the opportunity of being without nuclear power to focus on promoting renewable energy.

"Having zero running nuclear reactors is proof that we do not need nuclear plants," Junichi Sato, executive director of the environmental group in Japan, said on Friday.

He urged the government not to rush to restart reactors and to focus on containing the ongoing atomic crisis at Fukushima, and helping those evacuated to avoid exposure to radiation.