Anti-nuclear parties banded into a new political group on Wednesday, as Japan's fragmented electoral landscape shifts ahead of next month's national poll.

Three recently-sprouted parties and several independents merged into Nippon Mirai No To (The Future of Japan Party) on a platform of ridding the Fukushima-scarred country of atomic power.

The party is headed by high-profile regional politician Yukiko Kada, and its formation comes as opinion polls show the December 16 election is likely to leave no political party with sufficient seats to govern alone.

"We will create a new party, in response to people saying they don't have any party to choose from at the moment," Kada told a press conference near Lake Biwa, Japan's largest, in a region with a number of ageing nuclear reactors.

Japan must "graduate from nuclear power", the 62-year-old governor of Shiga prefecture in western Japan said. She later suggested a ten-year period would be required.

The governing Democratic Party of Japan (DPJ) on Tuesday declared its aim of weaning the country off nuclear power by the end of the 2030s.

Its opinion poll-leading opponent, the Liberal Democratic Party, has criticised anti-nuclear policies as "irresponsible" and unrealistic. The business-friendly bloc is broadly supportive of nuclear, which advocates say is essential if Japan is going to be able to power its industries.

Last year's tsunami-sparked disaster at Fukushima, where reactors melted down and spewed radiation into the air and sea, has engendered a vocal anti-nuclear movement in usually-quiescent Japan.

Ahead of next month's election of lower house lawmakers, small single-issue parties have mushroomed and the establishment of Nippon Mirai No To is an attempt to consolidate their fractured support.

Kada told reporters on Wednesday she wanted to field about 100 candidates and already had more than 70 ready to fight for the 480 available seats, with many more volunteers waiting in the wings.

The party was officially registered in Tokyo on Wednesday afternoon and boasts support from luminaries including Oscar-winning composer Ryuichi Sakamoto and management guru Kazuo Inamori, who helped rebuild Japan Airlines after it filed for bankruptcy.

Ichiro Ozawa, Japan's one-time political kingmaker who stormed out of the DPJ to form his own party earlier this year, was set to dissolve the group and join Kada.

The tiny Green Wind has also agreed to field its three former lower house members under Kada's umbrella, local reports said, as had one other small grouping.

Osaka mayor Toru Hashimoto and former Tokyo governor Shintaro Ishihara joined forces earlier this month to forge the Japan Restoration Party, which they say is a "third force" that can alter the direction of politics.