MONTREAL - In what has become an annual rite of spring in Montreal, authorities lobbed tear gas and moved in to break up an unruly mob protesting police brutality on Tuesday. When the dust had settled, 258 people had been arrested.

Police said numbers tallied after Montreal's notoriously raucous annual anti-police protest showed six people were arrested for alleged violations of the Criminal Code, 13 under municipal bylaws and 239 under the Highway Safety Code.

Several were detained even before the demonstration began, nabbed for infractions like carrying sticks and air guns on their way to the march. When the protest finally got underway, the crowd became increasingly restive as it marched away from the city's downtown core.

Minority of trouble-makers

A small minority of participants began hurling projectiles and some property was reported smashed, including cars and businesses. One person was hit in the face by a flying bottle.

Police eventually intervened. They fired tear gas and formed a human barrier to block off the crowd then moved in to make arrests.

But protesters pointed to the earlier arrests -- before the event began -- as a clear demonstration of why they don't trust police.

"They cited some municipal bylaw but, in any case, we know that it's an illegal preventive arrest and this is exactly why people are taking to the streets today," said event organizer Sarita Ahooja.

"This is why we are denouncing political profiling, we're denouncing racial profiling and why we're denouncing social profiling -- because it's discriminating against the way people think and believe."

A relatively orderly scene played out in Toronto, where the anti-police event was also held Tuesday. No arrests were reported there.

Toronto parallel protest

The Toronto demonstration was partly inspired by incidents at the G20 summit, where there were mass arrests and widespread allegations of police abuse.

Several dozen protesters waved black and red flags and recited chants from the G20 riots that ravaged the city's streets last summer.

Cries of "Whose streets? Our streets," rang through the air as protesters, who were outnumbered by authorities, stopped traffic while they stomped up Yonge St. toward police headquarters.

The crowd appeared to disperse peacefully, with a group of police officers following the few remaining protesters into the subway.

The scene was a bit edgier in Montreal -- but as far as that city's annual March 15th protest goes, it was par for the course.

Montreal's anti-police march typically spirals into vandalism and clashes with law enforcement, resulting in scores of arrests. There were 83 detained last year, and 221 in 2009.

Quiet residential streets were clogged Tuesday with police cars off the main arteries of the Plateau district. A helicopter buzzed overhead.

Those all in black

A group of protesters clad in the unmistakable uniform of a demonstration about to go awry -- head-to-toe black clothing -- moved along with the larger, mostly peaceful crowd.

The police forces in Canada's two biggest cities had been co-operating in preparation for Tuesday's events.

During last year's confrontation in Montreal, a Toronto police official was in the Montreal operations centre observing how it was handled.

Toronto police have also been sent information by the Montreal force to help them single out potential trouble-makers.

Montreal police say their force oversees 1,500 events a year and, each year, up to 98 per cent of them end without any incidents.

They blame the annual protest for sucking up a disproportionate share of police resources. Last year, during the Montreal event, they say that close to $500,000 was spent on police operations -- with $310,000 going to overtime for officers.

Police in out in force

On Tuesday, Montreal police were out in full force with helmeted officers on horseback and on bicycles. They also used Twitter to keep residents informed about where the demonstration was headed.

A number of officers wielding truncheons kept watch at the Place des Arts metro station, the starting point for the demonstration march.

People heading home during the afternoon rush hour were urged to avoid that downtown subway station.

The crowd headed north and east towards the Plateau, where traffic around several blocks was stalled during a standoff between police and the rowdiest protesters.

A voice finally blared out from the loudspeaker of a police vehicle, with a woman informing the crowd why they were about to be arrested: "(For)obstructing traffic on a public byway."

The protesters were thus read their rights, in both English and French, over a loudspeaker. They were informed they had a right to remain silent and to access a legal-aid lawyer.

Then, around 7:30 p.m., police moved in and escorted them into the paddywagon.

--With files from Alexandra Posadzki in Toronto