The unrest followed protests against the presence of United Nations peacekeepers in the country, as locals become increasingly angry over a cholera outbreak that many people blame on Nepalese troops.
The disease has killed more than 1,100 people in about three weeks.
Demonstrators set up burning barricades as vehicles were pelted with stones on Thursday. Several hundred rock-throwing youths attacked an open-top lorry carrying members of Minustah, the 12,000-strong UN mission in Haiti.
The young demonstrators, many of them in their teens, shouted slogans such as "Cholera: It's Minustah who gave it to us!" and "Minustah, go home" as the protests spread.
It was the fourth day the country had seen such demonstrations. The UN denies that it is responsible for the cholera outbreak. Earlier this week, at least two people were killed in riots against the UN in the north of Haiti.
Al Jazeera's Cath Turner in Port-au-Prince, said that rioting has escalated in the capital.
"The military wing of the national police have fired tear gas directly into the homeless camp across the road from the national parliament - Champ de Mars.
"Sources are telling us that there are scenes of parents and kids running around there trying to escape the tear gas.
"There are also UN troops monitoring this, and there are reports that they earlier fired tear gas at protesters. So really things are coming to a head now."
Hundreds of people have been living in tents in the Champ de Mars camp since January when a huge earthquake struck the country, particularly affecting the capital. More than 250,000 people died in the quake.
Some Haitians blamed Nepalese peacekeepers for the cholera outbreak, claiming that emanates from a base in central Haiti, where septic tanks have leaked into the Artibonite River, which locals use for drinking, washing clothes and bathing.
The UN insists that the Nepalese mission is not responsible for the outbreak, and linked the protests to the upcoming presidential election on November 28.
"The way the events unfolded leads to the belief that these incidents were politically motivated, aimed at creating a climate of insecurity ahead of the elections," the UN mission said earlier this week.
The significant anti-UN feeling appears to be growing in the country, with Haitians also blaming peacekeepers for a number of shootings in the country's second city of Cap-Haitien on Wednesday.
|Medical experts have warned that as many as 200,000 people could get cholera in the coming year [AFP]
However, a spokesman for Minustah, the UN mission in Haiti, told Al Jazeera there was no exchange of gun fire between UN troops and local residents.
Professor Peter Hallward, an expert in Haitian politics at Kingston University in the United Kingdom, told Al Jazeera that the UN mission was seen by many Haitians as an "occupying force".
"The UN has been there since 2004, to police the consequences of a coup, a coup that overthrew Jean Betrande Aristide, who was elected with a huge mandate several years before that." he said.
"It is seen as the force that came in to pacify the people and persuade them to accept this coup that was a violation of their sovereignty."
Hallward said he believed that Haiti would be able to function without the UN force.
"It didn't need the UN before, it didn't need the coup ... The fundamental problem here is that the coup overturned the political system, the continuity of a government that was trying to improve the situation of the people," he said.
Aid workers, including UN humanitarian agencies, said the unrest was hampering efforts to treat the tens of thousands of people stricken with cholera.
The Pan American Health Organisation/World Health Organisation said its Haiti country office had received reports of cholera victims dying in the streets because they were unable to reach health facilities in time.
"Cholera treatment is simple, but access is key," Dr Lea Guido, the PAHO representative in Port-au-Prince, said.
More than 18,000 people have been treated in hospitals and clinics since the mid-October outbreak, not including those who have died. According to medical experts, cholera could kill 10,000 people and cause 200,000 infections in Haiti in the coming year.
Source: Al Jazeera and agencies