TAIPEI (AFP) - A veteran Taiwanese opposition figure and human rights activist launched a bid on Thursday to stand for president next year, posing the latest threat to the embattled ruling Kuomintang (KMT) party.

Shih Ming-teh earned the title "Taiwan's Mandela" from local media after he was twice imprisoned by the KMT for sedition when it ruled the island under martial law.

The election will be a serious challenge to the Beijing-friendly KMT with its popularity waning due to fears of increased Chinese influence on the island.

A stagnating economy and a string of food safety scandals have added to its woes.

Shih announced his bid to stand as an independent candidate in the January vote which will also see Tsai Ing-wen of the main opposition Democratic Progressive Party (DPP) run. She would become Taiwan's first woman president if she won.

Shih - who was tortured in prison - is a respected rights activist due to his past campaigns for freedom of expression and against state violence under martial law. More recently he has argued for gay rights in Taiwan and has been a critic of mainland China's human rights record.

"Taiwan badly needs a Robin Hood president," said 74-year-old Shih, announcing his campaign.

He has criticised the two main parties for what he said were their cosy relationships with big business while workers' salaries have barely risen since the 1990s.

"If I get elected... wealth gained from injustice would be returned to the people," he said.

Shih also called for an end to the polarisation of the island between the KMT and DPP saying he would put together a "grand coalition government" of cross-party and independent talent.

- 'Robin Hood president' -

Shih faced recent controversy when he was criticised by gay and women's rights groups in 2011 for asking the DPP's Tsai to clarify whether she was gay. He argued that she should be open about her sexuality but Tsai said that answering him would make her an "accomplice of sexual suppression".

The political veteran, who was himself DPP party chairman from 1994 to 1996, was jailed between 1962 and 1977 for sedition after calling for Taiwan's independence from China and again between 1980 and 1990.

Shih now needs to get around 300,000 signatures from members of the public to become an official candidate, which his campaign team say they are confident he will do.

On Thursday Shih called for the maintenance of the "status quo" with China, but said both sides should commit to not using force against each other.

The island split from the mainland in 1949 after a civil war, but has never formally declared independence. Beijing still sees it as part of its territory, waiting for reunification by force if necessary.

The KMT are struggling to field a candidate after party leader Eric Chu announced that he would not run.

The party already suffered their worst-ever defeat in local elections in November.

Shih quit the DPP in 2000 and six years later launched a campaign against its graft-tainted then president Chen Shui-bian, galvanising hundreds of thousands of protesters to take to the Taipei streets.

Chen was imprisoned for 20 years in 2008 on corruption charges, but was released on medical parole in January.