By Aaron Sheldrick
TOKYO (Reuters) - More than 100,000 anti-nuclear protesters marched through central Tokyo on Monday to voice their opposition to atomic power, racheting up the pressure on under fire Prime Minister Yoshihiko Noda.
On the hottest day of the year, protesters forsook their air-conditioned homes to say the country does not need nuclear energy after last year's Fukushima disaster raised concerns about the safety of atomic power.
It was the biggest demonstration since Noda said last month Japan needed to restart reactors shut down for safety checks to avoid electricity shortages that might hit the economy.
"Today temperatures reached record high levels," Noda told Japanese television, as the city sweltered in 36.6-degree Celsius. "We must ask ourselves whether we can really make do without nuclear power."
Noda has come under increasing pressure amid growing public distrust of nuclear power, and his Democratic Party of Japan party was hit last month by mass defections after he pushed through an unpopular sales tax increase.
Noda's Democrats still control a majority in the lower house of parliament, but are outnumbered by the opposition in the upper house. Many analysts say mid-term elections could be called.
Protest organizers said 170,000 people turned out, closing one of Tokyo's main streets. Police estimated their number at up to 75,000, local media reported.
Most demonstrators were middle aged -- the constituency that has been the bedrock of support for the governments that ruled Japan during the growth years of the post-war era, powered by nuclear energy that many thought was cheap and safe.
"Japan is going to destroy itself by building nuclear plants in such an earthquake-prone country," said one protester, who gave only his surname, Saegusa.
All of the country's 50 nuclear reactors were taken off line after last year's earthquake and tsunami triggered 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 two reactors operated by Kansai Electric Power Co that passed widely criticized safety checks started earlier this month and another one is due to be fired up later this month.
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 Jeremy Laurence)