Tens of thousands of supporters of defeated presidential challenger Mr Lien Chan gathered to protest at Taiwan's presidential palace today as China warned it would not tolerate turmoil on the island.
Protesters defied chilly rain to demand a recount of last week's election, won by the incumbent by just 30,000 votes out of more than 13 million votes cast.
Mr Lien has also asked for an independent inquiry into an election-eve assassination attempt that lightly wounded Mr Chen and created a significant sympathy vote.
The rivalry between Mr Chen and Mr Lien threatens a prolonged crisis that could paralyse policy-making in one of Asia's most vibrant economies and in which the president governs but does not have a majority in parliament.
Beijing, which is anxious to prevent pro-independence activists who support Mr Chen's policy of greater sovereignty from using the turmoil to promote their cause, said it would not sit idly by if the protests got out of control.
Beijing regularly threatens to use force to recover an island it claims as a renegade province, but was unlikely to follow up its latest angry words with action.
It was using the rhetoric, which it had restrained for months to prevent stoking anti-China sentiment before the election, to warn independence supporters from disrupting today's demonstration, analysts said.
Beijing regards Chen and his pro-independence ambitions with grave suspicion and would clearly have preferred a victory by Mr Lien, who espouses a more conciliatory policy towards China.