TOKYO - Hundreds of Japanese anti-nuclear protesters gathered outside the prime minister's office on Friday, beating drums and chanting slogans against the planned restart of reactors a year after the world's worst nuclear disaster in 25 years.

"We oppose restarts," the crowd of about 1,000, which stretched for around 200 metres down the block, shouted in the peaceful demonstration.

Public mistrust of nuclear power has grown since the earthquake and tsunami on March 11 last year triggered the worst nuclear disaster since Chernobyl.

All of Japan's nuclear power plants, which once supplied about 30 percent of the country's energy needs, have been taken off line, leaving Japan vulnerable to power outages during the summer.

Prime Minister Yoshihiko Noda said on Wednesday said that it is necessary to restart idled reactors whose safety has been confirmed and that the central government is winning the understanding of local authorities.

A group of regional governors, long concerned about safety at the Kansai Electric Power Co's two reactors in Ohi, western Japan, signalled their agreement to the restarts as a "limited" step.