Protesters, wearing yellow headbands reading 'political persecution,' demanded justice for Chen, who has gone on hunger strike to protest what he says are politically motivated allegations against him.

Opposition Democratic Progressive Party (DPP) chairwoman Tsai Ing-wen took the stage briefly without addressing the crowd, as a pastor said a prayer to kick off the rally in a Taipei park.

'We are here to protest the Kuomintang government's political persecution of former president Chen and other DPP officials.... We demand protection of human rights and justice,' said organiser Lo Rong-kuang.

Organisers said about 10,000 people joined the event but a police estimate was not available.

Chen, who stepped down in May as president after serving the maximum eight years in office, still has a large following despite a string of scandals implicating him, his family and former top officials from his administration.

The ex-leader was hospitalised earlier this week for dehydration, days after going on hunger strike.

Two DPP magistrates accused of graft also went on hunger strike while in detention earlier this month to protest their innocence. One of the officials was later indicted on corruption charges while the other was released on bail.

Chen's lawyer is planning to bring his case to the island's grand justices after the High Court ruled an appeal against the ex-leader's detention invalid.

The lawyer submitted the appeal despite the ex-president's refusal as he felt such action was in his client's best interests.

Chen, whose pro-independence stance in office set him against Beijing, has repeatedly accused the island's China-friendly government of being behind allegations of embezzlement, money laundering, taking bribes and forgery.

He is the first former Taiwanese leader to be arrested, and could be held for up to four months before prosecutors have to charge him. -- AFP