Protesters mostly dressed in red to symbolise their anger Enlarge Image

The protesters, many dressed in red to highlight their anger, gathered in the capital on what organisers describe as the first day of mass protests.

Mr Chen's popularity has plummeted amid scandals involving relatives and aides.

In one case, his son-in-law is facing charges - which he denies - of insider trading on the stock market.

Organisers say more that 200,000 people joined Saturday's rally outside the presidential offices in Taipei - but police put the number at 90,000.

The BBC's Caroline Gluck, at the scene, says it is a sea of red.

There are four big red balloons, representing righteousness, integrity, prosperity and honour.

Chen protests gain ground In pictures: Taiwan protests

The protesters say these virtues have been lost in today's Taiwan, and Mr Chen should stand down.

The movement is led by Shih Ming-teh, a veteran activist who spent more than 25 years in jail when Taiwan was under martial law.

He says he is responding to a groundswell of public discontent.

Organisers say the protest is the first mass grassroots movement to remove a president that has not been organised by mainstream political parties.

However analysts say President Chen seems unlikely to stand down.

Last month he survived an unprecedented parliamentary attempt by the opposition Kuomintang to oust him.

The crisis began in May, when Mr Chen's son-in-law, Chao Chien-min, was detained on suspicion of insider trading.

Mr Chen's wife was also accused of questionable dealings.

The president has apologised for the actions of his son-in-law.