Thousands of demonstrators have rallied against the government's consideration of restarting nuclear reactors in the Japanese capital, Tokyo.

At least 7,500 people, including disaster victims and popular figures, gathered at a park in the city centre on Sunday, shedding light to the natural disaster two years ago that killed 19,000 and sparked a nuclear meltdown at the Fukushima Daiichi nuclear plant.

Prime Minister Shinzo Abe, whose Liberal Democratic Party has close ties with the nation's powerful business circles, has repeatedly said he would allow reactor restarts if their safety could be ensured.

Protesters later marched through the capital, holding anti-nuclear banners including one which read: "No Nukes! Unevolved Apes Want Nukes!"

They also demonstrated outside the headquarters of Tokyo Electric Power Co, operator of the Fukushima Daiichi nuclear power plant which was crippled by meltdowns after the March 2011 tsunami.

Kenzaburo Oe, Nobel literature laureate, was also among the protesters.

In March, more than 15,000 people gathered at the park demanding an end to atomic power two days before the anniversary of the disaster.

Japan turned off its 50 reactors for safety checks in the wake of the disaster but has restarted two of them, citing possible summertime power shortages.

Radiation from the plant, 220 kilometres northeast of Tokyo, spread over a wide area after the worst nuclear accident since the 1986 Chernobyl disaster.

Source: Agencies