Thousands of people staged anti-nuclear rallies in Japan Saturday as the country marked three months since its massive quake and tsunami which resulted in the world's worst nuclear accident in 25 years.

Radiation continued to leak from the crippled Fukushima Daiichi nuclear power plant, some 220 kilometres (140 miles) northeast of the capital, amid simmering public frustration over the government's slow response to the triple catastrophe.

Prime Minister Naoto Kan, under heavy pressure to step down, visited part of the disaster zone where 23,500 people were killed or are still unaccounted for while 90,000 others remained holing up in crowded shelters.

In the tsunami-hit port town of Kamaishi, Kan -- who was on his way to a memorial service -- was pressed by a fishery official to pass an extra relief budget as soon as possible. "I will work hard," the premier replied.

Media reports said that around 100 anti-nuclear events were staged nationwide, including in the western cities of Osaka and Hiroshima, which was devastated by a US atomic bomb in 1945.

In the capital an estimated 6,000 demonstrators, some carrying placards reading: "We don't want nuclear power plants" marched by the head office of the Fukushima plant's operator, Tokyo Electric Power Company (TEPCO), in a rally organised online by the Japan Congress against Atomic and Nuclear Bombs.

But dozens of apparently right-wing activists, some of them holding the military rising-sun flag, jeered from the roadside condemning the calls to downgrade Japan's nuclear ambitions.

TEPCO, once the world's biggest utility, has seen its share price plunge more than 90 percent since the March 11 disaster.

A minute's silence was observed at various places nationwide at 2:46 pm (0546 GMT), the moment the 9.0-magnitude quake struck below the Pacific seafloor sending monster waves over the country's northeastern Tohoku region.

"It is time to shift to renewable energy sources," Greenpeace director Kumi Naidoo told a rally at Tokyo's Yoyogi Park before they took to the streets holding sunflowers and gerbera daisies.

"I have yet to have a child but I come here with my neighbours and their children because of the fear we feel every day," Misuzu Kiyozumi, a 34-year-old housewife from the suburban city of Ichikawa, told AFP.

The prime minister attended a meeting with leaders in Kamaishi on ways to improve survivors' lives while newspaper editorials criticised his government's handling of the calamity.

"I heard what they really need. I want to incorporate into a second supplementary budget what has not been included in our first supplementary budget," Kan told reporters after the meeting.

The mass-circulation Yomiuri Shimbun said his government's assistance to disaster-hit communities "has been insufficient."

"The removal of rubble has been overly delayed. Construction of makeshift housing for evacuees has yet to get on the right track," it said.

Rebuilding the muddy wastelands of the Tohoku region -- an area now covered in 25 million tonnes of rubble -- will take up to a decade and cost hundreds of billions of dollars, experts say.

A 20-kilometre (12-mile) no-go zone has been enforced around the Fukushima nuclear plant, which emergency crews hope to bring into stable "cold shutdown" between October and January.

Environmental and anti-nuclear group Greenpeace called on Japan this week to evacuate children and pregnant women from Fukushima town, about 60 kilometres from the stricken plant, because of what it said was high radiation.

Since the disaster, Japan has raised the legal exposure limit for people, including children, from one to 20 millisieverts per year -- matching the safety standard for nuclear industry workers in many countries.

In the wake of the disaster, Kan has said resource-poor Japan will review its energy policy, including its plans for more nuclear reactors, while making solar and other alternative energies new pillars of its energy mix.