MONTREAL -- A Montreal anti-racism protest demanding justice for a black Minnesota man who died following a police intervention last week degenerated into clashes between police and some demonstrators on Sunday night.

About three hours after a march that snaked its way through downtown Montreal on Sunday afternoon had ended, Montreal police declared the gathering illegal after they say projectiles were thrown at officers who responded with pepper spray and tear gas.

Tensions flared after the formal rally had concluded and some demonstrators made their way back to the starting point, in the shadow of Montreal police headquarters downtown.

Windows were smashed, fires were set and the situation slid into a game of cat-and-mouse between pockets of protesters and police trying to disperse them.

Demonstrators had gathered to denounce racist violence and police impunity -- both in the U.S. and at home in Montreal.

George Floyd died in Minneapolis on Monday after pleading for air while a white police officer pressed a knee on his neck.

His death has sparked nightly protests in major U.S. cities.

The Montreal rally was a solidarity gathering with American anti-racism activists, but organizers say it is also an opportunity to express their own anger at the treatment of racialized people in Quebec and elsewhere in Canada.

Some of the names invoked included names of black men killed during Montreal police interventions in recent years.

"It's important for everyone to be here today so that we can have a lot of voices to say the George Floyd event is not a singular event," said Marie-Livia Beauge, one of the event organizers. "It keeps happening and it's happening here in Montreal so to be here together is to show solidarity and denounce the injustice."

The gathering drew Montrealers of all stripes and backgrounds, holding posters with slogans. Protesters chanted "Black lives matter" and "I can't breathe" -- what Floyd was caught on video saying.

They took a knee in unison several times in solidarity with the movement.

Mousseau called out Montreal Mayor Valerie Plante, who earlier Sunday had condemned "violence, racism and systemic discrimination."

But one speaker cautioned against empty words from leaders.

"In fighting this, we need to ensure our movements are not co-opted to stifle our anger with their kind word and simultaneous inaction," said Vincent Mousseau, a social worker and community organizer.

During the COVID-19 pandemic, organizers repeatedly told people to spread out, trying to find a spot where a two-metre distance could be maintained.

Despite a majority of people wearing masks and organizers squirting hand sanitizer, the numbers attending made distancing impossible.

The location adjacent to Montreal police headquarters was packed, with police closely guarding the building that houses their brass.

Dr. Horacio Arruda, Quebec's director of public health, told Radio-Canada on Sunday evening that he recognized the importance of the cause but urged hand washing and for anyone exhibiting symptoms to let health authorities know they attended the protest.

Around the start of the demonstration, Montreal police took the unusual step of issuing a tweet saying they were dismayed by the death of George Floyd.

"Both the action taken and the inaction of the witnesses present go against the values of our organization," the force tweeted calling on for a peaceful demonstration.

"We respect the rights and the need of everyone to speak out against this violence and will be by your side to ensure your safety," the police said.

The Montreal rally followed one in Toronto on Saturday, which remained peaceful.

So too did Sunday's rally in Vancouver, where thousands gathered outside the city's art gallery, waving signs and chanting their support of the Black Lives Matter movement and Floyd.

Tristan Miura, who held up a skateboard painted with the words "injustice anywhere is a threat to justice everywhere," said he hopes Vancouver will reflect on the protesters' message.

"Vancouver has always been quite liberal and very open about what they feel is wrong in the community," said Miura. "I think Vancouver, as a whole, is taking this time to reflect on past issues and preventing further issues from occurring."

Others hoped it would spark a larger reaction in Canada.

"I hope this is just the start," said Chance Lovett. "I hope this is just the beginning of a larger conversation and a larger movement."

Vancouver police said there have been no arrests during the event.

This report by The Canadian Press was first published May 31, 2020.

With files by Nick Wells in Vancouver.