A massive climate rally in downtown Montreal has drawn tens of thousands of protesters to the city’s streets on Friday as students and workers hold walkouts to fight for the environment.

Greta Thunberg, the 16-year-old Swedish activist who has become a star of the environmental movement, is leading the protest. She spoke ahead of the demonstration at a press conference on Friday morning, saying it was moving to see so many people take part in the fight against climate change.

“To once again stand together, people from all around the world, for one common cause, that is very empowering,” she said.

The march against climate change, which kicked off in the afternoon at the Georges-Étienne Cartier statue in Mount-Royal Park, is also being attended by several federal party leaders.

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Thunberg called on Canada to take responsibility to protect the environment and she also had a message for political leaders in the country. She also sat down briefly with Liberal leader Justin Trudeau on the sidelines of the march.

“My message to all the politicians is the same: listen to the science, act on the science,” she said.

Quebec Public Security Minister Geneviève Guilbault has called for calm ahead of the demonstration.

“We expect a lot of people, especially in Montreal, also in Quebec City,” she said on Thursday. “As with any type of public event of this size, a public gathering of this size, the message that is important to pass is to remain respectful of the rules, to remain peaceful, to remain calm, to remember the reason why we’re meeting.”

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The protest is expected to snarl traffic in Montreal, but efforts have been made to ease congestion. Public transit will be free for the day, and commuters in Laval and the city’s south shore will also be able to use public transit free of charge.

“If you are are driving and you’re used to driving downtown, don’t use your car,” said Montreal Mayor Valérie Plante on Thursday. “That is really the message.”

Montreal police advised residents to carefully plan their commute, saying traffic will be hard to get around the downtown core between Berri, Peel, St-Joseph and de la Commune streets.

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Ahead of the climate march, several universities and CEGEPs in Montreal have cancelled classes. Included among them are Dawson College and John Abbott College. Concordia University has cancelled classes for the afternoon.

The Commission Scolaire de Montréal — the province’s largest school board — has also cancelled class for elementary and high school students. The Lester B. Pearson School Board says the day is already a designated pedagogical day.

More than 140 climate protests are planned across Canada. The Montreal event is expected to draw a heavy youth presence and organizers estimate up to 300,000 protesters could show up.

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— With files from Global News’ Rachel Lau, Amanda Jelowicki and The Canadian Press