TAIPEI, Taiwan (AP) - A half million people swarmed into Taiwan’s capital on Saturday to protest the disputed presidential election, while China hinted that the turmoil might provide a reason for it to take control of the island.

Demonstrators wore yellow rain ponchos in the cold drizzle and waved Taiwanese flags as they filled the wide boulevard outside the Presidential Office. They cheered and listened to fiery speeches that alleged President Chen Shui-bian rigged the March 20 vote.

The rally started peacefully - a contrast from the day before when about 2,000 people stormed the Central Election Commission headquarters in Taipei. The mob broke glass windows and scuffled with police in an unsuccessful attempt to delay the formal certification of the election’s results.

The losing candidate, Nationalist leader Lien Chan, addressed the crowd and repeated his demands for a recount of the vote that Chen won by a tiny margin.

``If someone uses nasty means to gain power, such power won’t be effective and won’t be respected,’’ said Lien, a 67-year-old former political science professor and ex-vice president.

Lien also demanded an independent investigation into the bizarre election-eve shooting that lightly wounded Chen and might have given him a crucial last-minute boost at the polls.

His running mate James Soong told the crowd that if a new election is held, he’d be willing to give up his candidacy for vice president to prove that he was motivated by a desire for a fair vote, not by a hunger for power.

Those who believed conspiracy theories that Chen staged the shooting to gain sympathy votes carried signs that said, ``Democracy shot in the stomach’’ and ``Shooting tricks shall be revealed.’’

After Lien’s speech, ruling party lawmaker Hsiao Bi-khim expressed disappointment that Lien and Soong didn’t tell the crowd that the president has already agreed to a recount and an independent investigation.

Hsiao also noted that the opposition candidates didn’t say whether they would accept the results of a recount. ``This is really regrettable,’’ she said.

Police said about 500,000 people attended the rally.

Chen was officially declared the victor by the Election Commission on Friday, drawing a statement of congratulations from the United States that was condemned by China.

``We congratulate Mr. Chen on his victory,’’ White House press secretary Scott McClellan said, while recognizing the pending legal challenges of the results.

China expressed displeasure Saturday over Washington’s message, saying it was an ``incorrect act’’ that undermined its commitment to Beijing’s one-China policy. China still claims the island as its territory although the two sides split during civil war in 1949.

The admonition came one day after Beijing said it wouldn’t ``look on unconcerned’’ if the turmoil in Taiwan continued. China didn’t say what it might do, and it wasn’t clear whether the comments were more than a ritual declaration of the mainland’s rights over the island. Beijing previously has threatened to take over the island if it ever descends into chaos.

Taiwan’s government warned China against meddling in its affairs.

The president, who campaigned on a platform of standing up to China, has agreed to a vote recount, but lawmakers disagree about how to amend election laws to allow for a speedy re-tally and who should examine the ballots.

One of the most difficult tasks for Chen might be satisfying the many skeptics who believe he faked the shooting.

Police haven’t made any arrests, but on Friday sought the public’s help by releasing photos captured by security cameras of a man hurrying away from the shooting scene.

The president’s Democratic Progressive Party urged supporters to avoid the rally and refrain from displaying the party’s logo.

Chartered buses from cities in southern Taiwan arrived for the rally, as protesters said Friday’s violence didn’t scare them away.

``That was a small minority of overexcited people. We still know our demands are reasonable, so we still have to persist and stay here,’’ said Colin Wu, 38, an insurance salesman.

Some protesters held up pictures of Chen and the vice president as others beat the images with umbrellas. Many wore black, as requested by the Nationalist Party, to symbolize mourning for Taiwan’s democracy.

``This was a very dirty election. We want the truth,’’ said Carla Wang, a 56-year-old who works at a trading company.

The brown-brick Presidential Office was ringed by police buses, while streets leading to key government buildings and to the ruling party headquarters were barricaded.

At the tall marble Nationalist Party headquarters facing the Presidential Office, protesters were picking up white balloons with the word ``Recount.’’

``This is a moment in history I cannot let pass,’’ said Eve Chiang, 29, a sales assistant at a clothing store, waiting to receive a balloon.