TORONTO - - Ten thousand people marched against the G20 summit Saturday to protest for jobs and social causes, in a largely peacefully rally that saw nevertheless saw outbreaks of violence on its fringes.

A protester gestures towards riot police while marching along the streets of downtown Toronto during the G20 Summit on Saturday, June 26, 2010. (AP Photo/The Canadian Press, Nathan Denette) While the main body of the march was a well-marshaled event, led by older activists and organized labor, small groups of young hardliners scuffled with riot officers and set fire to at least two patrol cars.

In addition to the two which were set ablaze, at least three more cars were damaged in downtown Toronto's financial district, and the air was thick with the smell of vinegar-soaked rags used to ward off police tear gas.

Firefighters moved to douse the flames, but there was chaos nearby as businesses dropped their shutters and bystanders were caught up in the action.

Lara Garrido Herrero, 33, a weekend visitor to the city who was shopping in the downtown Eaton Center mall, told AFP by telephone: "Around 200 people are stuck in a lock-down in the shop and the staff are handing out water."

Toronto police used the microblogging site Twitter to deny a rumor that rioters had breached the security barrier erected around the conference center where the leaders of the world's richest countries were gathering.

"Dispelling more rumors: The fence has not been breached. False reports," the message read.

Canada spent more than a billion dollars to secure this week's back-to-back G8 and G20 summits, hoping to avoid the serious street battles that have marred most recent gatherings of these global forums.

Thousands of police reinforcements backed by riot officers on horseback and spotter helicopters have been drafted into the city center, much of which is sealed off behind concrete and steel barriers.

The marchers stood for an hour on the lawn of a government building in downtown Toronto, braving cold and rain to cheer on labor leaders and others who urged the G20 to put people ahead of financial institutions.

"It wasn't the workers of the world that caused the financial crisis," Sid Ryan of the Ontario Federation of Labour said in a speech. "We don't want to see a transfer of wealth from the public sector to the private sector."

"The people, united, will never be defeated," steelworkers and their unionized brethren shouted back, placards poking through rips in a tapestry of umbrellas that read: "Long live socialism" and "Scrap the summits."

Already at daybreak, about 50 protesters were keeping vigil in a wooded tented encampment in downtown Toronto, and maybe another 50 had already moved off towards Queens Park for the start of the main rally.

One of the campers covered himself in baby oil, offered to wrestle bystanders and climbed a tree -- to the amusement of the world's media but the annoyance of protesters, who thought he distracted from their causes.

"I hate him, but I have to admit he probably has great skin," said one female protester.

They would soon be joined by 30 busloads of unionized workers from across Ontario province, as well as supporters of Oxfam, Greenpeace, the Canadian Federation of Students and the Council of Canadians.

By midday, the crowd had ballooned to 10,000, said organizers, citing authorities' official estimates.

Their issues include the legitimacy of the G20 itself, and jobs. "We don't want G20 countries to cut stimulus spending until jobs recover," Jeff Atkinson, spokesman for the Canadian Labour Congress, told AFP.

Greenpeace International Director Kumi Naidoo argued that if G20 countries could spend billions of dollars to rescue banks in trouble, why not find money to help unemployed workers, for the environment and for social causes.

Student activist Liana Salvador lamented that she was 50,000 dollars in debt for school. "I'm an ordinary student whose parents taught me that knowledge is power, but whose government says education is just expensive."

"Do only the rich deserve to learn?" she demanded.

"One billion for education, not fortification," she shouted, lamenting the billion-dollar cost of securing the G8 and G20 summits in the Toronto area.

"Let's come together and unite the labor movement, the environmental movement, the women's movement... and we can move mountains," Ryan said.

Police on bicycles and on foot kept watch, but they were less visible than on Friday for an earlier march.

Demonstrators released balloons in the air, and there was music and dancing. But while mostly peaceful, the protest had a serious air.

Sergeant Tim Burrows, spokesman for the Integrated Security Unit responsible for securing the summit, said 32 people had been arrested since June 18 for "G20 related incidents."

They faced 51 charges, including assaults on policemen at the Friday rally, wearing disguises near G20 barricades, weapons and immigration violations, and involvement in three separate bomb plots, said Burrows.