MONTREAL -- Downtown Montreal was once again the scene of arrests as demonstrators crashed the Formula One Grand Prix party.

Montreal cops confirmed 12 arrests overall Friday night, some of which were made near restaurants and terraces crowded with F1 fans.

The crowd of festival goers on Crescent Street between De Maisonneuve and Sainte-Catherine Street was estimated at nearly 20,000 people.

A score of protesters equipped with pots and wearing the red square emblematic of the movement had managed, despite a heavy police presence, to infiltrate the festivities.

At some points, protesters and festival goers came to blows and police had to use pepper spray to disperse the crowd. Some were arrested.

The demonstration ended shortly before 1 p.m.

Montreal has been in the international spotlight for months due to its massive -- and sometimes destructive -- student movement of those who oppose Premier Jean Charest's plan for a $1,800 tuition increase over seven years. The movement gained a new target last month in Quebec's controversial bill 78, which was passed in response to the unrest.

The Grand Prix has become a top target for a coalition of radical students and anti-capitalists.

The website of the hardline CLASSE group calls on followers to oppose the "capitalist elite" at the Grand Prix, an event they dismiss as "sexist, non-environmental and economic."

The president of the Merchants Association of Crescent Street, Bernard Ragueneau, said protesters created some "cacophony", but they weren't numerous enough to disturb the ongoing activities.