PORT-AU-PRINCE -- Supporters of President Jean-Bertrand Aristide blocked streets with burning tires and debris Friday as his opponents mounted a second day of marches to demand his resignation.

Thick black smoke billowed from dozens of intersections in the capital as groups of Aristide supporters, some armed with shotguns and rifles, crammed into the beds of battered pickup trucks and roamed the city.

The president's backers surrounded the National Palace and dared the opposition to show up.

''Tell them to come over, we're waiting,'' said a defiant Harold Nicholson Veillard, 34. ``Tell the bourgeoisie if they don't like it they can leave the country.''

There were unconfirmed reports of at least one person shot in Port-au-Prince, and countless others struck by rocks. The protests extended outside the capital, from the southern city of Jacmel to Gonaves in the west.

The unrest forced U.S. Rep. Kendrick Meek and other members of Congress to cancel a visit on Friday. Meek and the others had planned to look at the efforts of the Organization of American States and humanitarian programs in Haiti.

Police did not stop pro-government demonstrators as they set the tires, wood and other debris ablaze in the middle of normally bustling streets. The burning barricades forced drivers to turn their vehicles around and kept pedestrians boxed into confined areas. Streets in some sections of the capital were almost deserted as businesses closed and people stayed home.

Young men and boys, some wielding baseball bats and sticks, manned checkpoints at which motorists were stopped and questioned throughout the day.

The government backers appeared to be working with police to keep the anti-Aristide forces from a repeat of the massive demonstration held the previous day.

On Thursday, more than 50,000 demonstrators, by some estimates, marched through the city calling on Aristide to resign. The protest, said to be one of the largest in a decade, followed a student-led protest several days earlier that turned violent.

Although Friday's protests were smaller, it was equally as confrontational, with demonstrators and police clashing.

''What we want is to exercise our freedom of speech,'' said Valerie McIntosh, 32, a communications and marketing specialist who opposes Aristide. ``This is supposedly a democratic country. But they won't even let us march.''

McIntosh removed her sunglasses to reveal her watery eyes. She said police tear-gassed her for attempting to exercise her right to peaceful protest. She expressed worry that the world, preoccupied with such hot spots as Iraq and Afghanistan, is oblivious or unconcerned with the worsening economic, social and political situation in Haiti.

''The people need to know what's going on,'' she said. She added that Haitians in Miami and New York do not seem to be moved by unfolding events on the island.

McIntosh was among hundreds of demonstrators in the suburb Petionville who clashed with police. Clad in riot gear, the police were attempting to protect members of Aristide's Lavalas Family Party. The police action set off stampedes through the streets.

''We want freedom of expression, we want democracy, we want to be able to live as human beings,'' said Stanley Joseph, 43, a businessman. ``Aristide was supposed to be the champion of the cause, but he ended up being a tyrant and a murderer.''

Paul Antoine, a spokesman for Aristide, said Friday the president was ''monitoring the situation'' and had no immediate plans to respond to the latest events.

Culture and Communication Minister Lilas Desquiron took to the airwaves to appeal for calm. She blamed a media ''disinformation campaign'' for the mounting protests.

But on Friday, Dany Toussaint, a Lavalas senator, announced he was quitting the party. ''I am no longer a Lavalas senator,'' he announced on the radio. This, after he referred to the government as ''despotic'' and a ``fascist Creole regime.''

Aristide on Thursday condemned the violence, called for calm, and again urged the opposition to participate in next year's legislative elections. The opposition has said it will boycott because of alleged improprieties during the 2000 legislative elections.

Aristide, whose term ends in 2006, has said a vocal minority is behind the protest. He has vowed to serve out his term.