Japan has restarted a nuclear reactor for the first time under new safety standards put in place since the Fukushima disaster in 2011, as Prime Minister Shinzo Abe seeks to reassure a nervous public that the industry is now safe.

Abe and much of Japanese industry want reactors to be switched on again to cut fuel bills, but opinion polls show a majority of the public oppose the move after the nuclear crisis triggered by the earthquake and tsunami four years ago.

Kyushu Electric Power began the restart on Tuesday of the No. 1 reactor at its Sendai plant, a spokesman said. The reactor will take a few days to reach full power if all goes to plan.

The head of Japan's atomic watchdog said that new safety rules meant a repeat of the Fukushima disaster would not happen, but protesters outside the Sendai plant are not convinced.

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