Dozens of protesters were arrested in Halifax and Toronto, and fist fights reportedly broke out in Edmonton Monday morning as climate change activists blockaded several major commuter bridges in Canadian cities.

The demonstrations were part of efforts by Extinction Rebellion Canada that snarled rush-hour traffic for thousands of people, and included protests in Halifax, Toronto, Edmonton, Kitchener, Ont., Victoria and Vancouver.

Demonstrators are demanding that Canada and the provinces bring in policies that will see the country's carbon emissions reduced to "net zero" within six years.

Halifax police said they arrested 18 protesters shortly after 11 a.m. AT. Each faced a charge under Section 4 of the Protection of Property Act. Police said those taken into custody had refused to leave after shutting down the Macdonald Bridge over Halifax harbour for 3½ hours.

In Toronto, dozens of protesters prevented motor vehicles from crossing the Bloor Viaduct on Monday morning. Traffic was blocked at Broadview and Danforth avenues, and more demonstrators were set to close lanes around Castle Frank Station, on the other side of the bridge.

Demonstrators paint the roadway on Toronto's Bloor Viaduct during the shutdown. (Mark Bochsler/CBC)

Const. Caroline de Kloet told CBC News in an email that 20 people were arrested, but did not share any other details.

Cyclists were able to use the bridge's bike lanes. Subway service was unaffected.

Holding signs and banners, demonstrators blocked crosswalks at a Kitchener. Ont., roundabout Monday morning, bringing traffic to a stop intermittently during the busy morning commute. The protest wrapped up around 9 a.m. ET.

Emily Steers, 23, one of the participants in the Kitchener protest, said she was there "because I'd like to have a future. For any children I'd like to have ... we are trying to preserve our world."

Rush-hour blockades in B.C.

In Vancouver, more than 100 climate activists gathered in the morning's downpour before crossing the Burrard Street Bridge just after 9 a.m. PT. The group unfurled a red banner at the northern end of the bridge, an arterial link between southern end of the city and the downtown core, and blocked traffic in both directions.

In Victoria, organizers had also planned to gather on the Victoria side of the Johnson Street Bridge at 3:30 p.m. PT to block afternoon commuter traffic until 6 p.m.

"Mostly we want people in power to listen and if [people are] inconvenienced we're really honestly sorry about that but extinction and the kind of impacts of the climate crisis are going to be a huge inconvenience," said organizer Mark Nykanen.

Protestors are now moving onto the bridge. Organizers asked who would be willing to risk arrest, about two dozen came forward to carry a large flag. <a href="https://t.co/KsSk2F5mcv">pic.twitter.com/KsSk2F5mcv</a> —@_rossandrea

'Very ticked off commuters' in Edmonton

While protests were mostly peaceful in Halifax and Toronto, drivers in Edmonton, where the Walterdale Bridge was shut down, were less tolerant.

About 10 protesters with hands linked began blocking the three lines on the bridge at 7 a.m. MT, as a line of waiting vehicles began to snaking up the length of Walterdale Hill and Queen Elizabeth Park Road.

Edmonton police were on scene as climate action demonstrators staged a blockade on Walterdale Bridge during morning rush hour. (Dave Bajer/CBC)

A revving motorcycle drove around the line of protestors. Another driver attempted to swerve around the demonstrators while repeatedly honking his horn. Bicycles the protesters had placed along the road as a barrier were thrown to the curb.

Other drivers approaching the Walterdale Bridge exited their vehicles to scream and curse at the demonstrators. The protest wound up at about 8:15 a.m.

"I think there were some very ticked off commuters to say the very least," Staff Sgt. Neil Thompson said in an interview with CBC News.

"I think there might have been some fists flying, but I think that stopped fairly quickly."

Ten protesters blocking Walterdale <a href="https://twitter.com/hashtag/yeg?src=hash&ref_src=twsrc%5Etfw">#yeg</a> pleading w/police to move protesters <a href="https://t.co/XXWSr5lLnk">pic.twitter.com/XXWSr5lLnk</a> —@LydiaNeufeldCBC

Vent frustrations to politicians, Halifax protester says

In Halifax, the bikeway and pedway on the Macdonald Bridge were closed, causing lineups at a nearby ferry terminal. A couple of hours into the rally, the number of protesters in the Nova Scotia capital had swelled to more than 150.

Halifax police said the decision to close the bridge, including the bikeway and pedway, was made in conjunction with Halifax Harbour Bridges for public safety reasons.

Patrick Yancey, with the Nova Scotia chapter of Extinction Rebellion, said he empathized with people not able to use the bridge and said they should direct their frustration to politicians.

"They certainly should not be having to deal with this situation. None of us should be — this should have been solved a long, long time ago. We encourage them to vent their frustrations to their MLAs, their MPs, their premier and prime minister as well. Hopefully, we'll not have to do this sort of thing again."

The scene now as police block the protesters from accessing the MacDonald Bridge. Have talked to pedestrians and cyclists upset they can't use the lanes. Police closed that. <a href="https://t.co/h9Sj37VRTV">pic.twitter.com/h9Sj37VRTV</a> —@cbccolleenjones

'Very important moment'

Robert Huish, an associate professor at Dalhousie University who studies the impacts of climate change, said Monday's bridge protest is a "very important moment."

He noted it comes on the heels of street protests that have drawn millions of people worldwide, to demand urgent measures to avert an environmental catastrophe.

"Right now that form of protest, that solidarity, was one about bringing people together," Huish said in an interview last week.

"Now we're stepping into a different territory come Monday when the bridge is planned to be blocked, and that is one that is going to be a bit more aggressive and intentionally inconvenient.

"The message is now changing a bit from being, 'Let's all be together,' to say we're now going to create an inconvenient space to recognize just how inconvenient climate change really is."

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