By Aaron Sheldrick
TOKYO (Reuters) - More than 15,000 anti-nuclear protesters blocked streets outside the Japanese prime minister's office on Friday, beating drums and chanting slogans against the restart of reactors nearly 16 months after the world's worst nuclear disaster in 25 years.
The crowd blocked off a six-lane road and adjoining streets leading to the Prime Minister Yoshihiko Noda's official residence in central Tokyo. Police parked five armored riot control buses in front of the entrance to prevent protesters entering the compound.
Several helicopters circled overhead as the sun went down on a clear, early summer evening.
The protest capped weeks of sporadic demonstrations and was the biggest gathering in central Tokyo since Noda said this month the restart of two reactors in western Japan was necessary to avoid damaging the economy.
All of the country's 50 nuclear reactors were taken off line after an earthquake and tsunami hit the Fukushima nuclear power plant on the northeast coast on March 11 last year, triggering the world's worst atomic accident since Chernobyl in 1986.
Nuclear power had previously supplied nearly 30 percent of Japan's electricity.
The first of the two Ohi reactors operated by Kansai Electric Power Co is scheduled to be reactivated on Sunday.
The crowd, including office workers, mothers with children and elderly people, chanted "oppose restarts" and "exit nuclear power".
The decision to restart the reactors as summer power-cuts loom was seen as a victory for Japan's still-powerful nuclear industry.
But Japanese people have grown wary of nuclear power since Fukushima, with surveys showing that about 70 percent want to abandon atomic energy even if not immediately.
(Editing by Robert Birsel)