Police said a mix of communists, anarchists, skinheads and members of other groups estimated to number 700 to 800 people began a peaceful anti-capitalist protest Sunday afternoon, The (Montreal) Gazette reported.
Six people were arrested for minor infractions and after seven police officers suffered minor injuries the march was stopped because it was "no longer peaceful," Montreal police Constable Raphael Bergeron reported.
Before the march began, Alain Simoneau, the police commander, addressed the protesters on a loudspeaker, saying they would be allowed to proceed as long as they followed the direction of traffic and were peaceful.
He told them if there were any infractions authorities would "put an end to the demonstration."
About 4:10 p.m., someone lit a flare and threw it at police and officers moved in and broke up the protest, the Gazette reported.