About 300,000 opposition supporters in Taiwan have been holding a fresh protest against the narrow re-election of President Chen Shui-bian last week.
The opposition want a recount
Braving the rain, they gathered outside the presidential palace a day after President Chen's victory was confirmed.
Mr Chen's opponent, Lien Chan of the Kuomintang party, vowed to continue the protests "until our goal is achieved".
Mr Lien, who has demanded a recount of the vote, urged supporters to remain calm and prepare for the long haul.
On Friday, opposition activists clashed with police and stormed the offices of Taiwan's election body.
China, which regards Taiwan as part of its own territory, says it will not stand by if Taiwan descends into chaos.
Taiwan has told China not to interfere.
A spokesman for US President George W Bush, Scott McClellan, urged Beijing and Taipei to pursue dialogue and refrain from unilateral steps that would alter Taiwan's status.
He said the US would continue to maintain close ties with Taipei.
Later, Beijing denounced as a "mistake" a US message congratulating Mr Chen after his narrow re-election was formally confirmed on Friday.
President Chen was re-elected by a margin of only 0.2% of the vote, hours after an apparent attempt to kill him, which the opposition says unfairly influenced the election.
Dressed in black in a sign of mourning and standing in front of a huge sign reading "Democracy is Dead", Mr Lien said there had been more than 1,000 irregularities in the vote.
"Our common demands are very simple: immediate recount. I want to ask Mr Chen Shui-bian: What are you afraid of? Stand up!"
Appealing to his supporters to remain calm, Mr Lien said the opposition struggle had to be "flexible", interacting with President Chen on a long-term basis.
"We must be prepared for a long battle," Mr Lien said. "We will not end our struggle until our goal is achieved. We must let the world see the power of the people."
He told the crowds their protest would continue unabated as Mr Chen and his government "is obviously planning to wait in comfort for an exhausted enemy".
"If there are still no responses in mid-April and late-April, that will mean he wants to invite us to the so-called inauguration ceremony" on 20 May, Mr Lien said.
"Then maybe a lot of people will be very pleased to come and see what it is all about," he threatened.
Thousands of extra police have been deployed for the protest.
The mayor of Taipei, Ma Ying-jeou, has said any protest that goes on past 1000 GMT will be declared illegal and dealt with by the police.
Organisers of the rally have urged their supporters to disperse before nightfall.
President Chen has agreed to meet opposition leaders as well as their demands for a recount.
But lawmakers have so far failed to reach agreement on how to amend election laws which would allow for a speedy recount.
Police investigating the attempted assassination of the president have released the first images of an unidentified man walking away from the scene where he was shot.
The attempted assassination is "suspicious", the opposition alleges
The grainy images from a closed-circuit TV camera showed a balding, middle-aged man in a yellow jacket and blue trousers walking briskly away from the scene.
Police said there was no other evidence to link him to the attack, but they wanted to identify him.
The opposition say the suspicious circumstances surrounding the shooting - and alleged irregularities - one day before the vote cost them the election.
President Chen has said the assassination attempt was genuine and rejected allegations of vote-rigging.