Three environmental activists surrendered and were taken into custody after climbing Montreal's Jacques-Cartier Bridge in a protest Tuesday morning that prompted provincial police to close the structure off to traffic.

The protesters, two women and a man with Extinction Rebellion Québec, had begun climbing the bridge before sunrise, and surrendered just after 8 a.m. ET. Traffic was moving again in both directions by 8:40 a.m.

"You can arrest people, but it won't change the problem of climate change," said Louis Ramirez, a spokesperson for the environmentalist group.

"The science is now dead clear, and what we're now seeing is lives are in danger. Hundreds of millions of them."

The stunt was part of a series of protests Extinction Rebellion has staged so far this week, including blocking other bridges across Canada Monday. More than 100 protestors also joined a demonstration in downtown Montreal Tuesday evening.

Their route was blocked by police, stalling on René-Lévesque Boulevard at the corner of Metcalfe Street for several hours and into the night. Police arrested about 40 people at around 10:30 p.m. after warning them to clear the way. Some had been lying in the street for an past hour as part of the protest.

Police moved in to arrest about 40 protesters in downtown Montreal Tuesday at around 10:30 p.m. (Radio-Canada)

The group said achieving "climate justice" will require continued, massive political action and that, so far, the hundreds of thousands of people who have mobilized to protest climate change in Quebec are being ignored.

"This planet cannot hold six billion people if we keep going like this. It's pretty simple," François Léger-Boyer of Extinction Rebellion told reporters at the evening protest.

"People are fed up with inaction. They want the politicians to take drastic actions to reduce CO2 emissions."

One of the three protesters on the Jacques-Cartier bridge earlier in the day made a live video broadcast on Facebook from the top of the bridge, saying the aim of the action was to "disrupt the social order" so authorities will listen.

Down below, a handful of protesters gathered on the bridge's bicycle and pedestrian path to hold signs and chant support for the climbers.

Louise Desrosiers, a spokesperson for Montreal's fire department, said firefighters are "always ready for these types of interventions."

The department's high-angle rescue team climbed the bridge to monitor the situation.

The protesters were calm but had no intention of leaving the bridge, Desrosiers said. Rescuers remained near the protesters until police could step in, she said.

Watch this video footage capture at the Jacques-Cartier Bridge:

A handful of protesters from Extinction Rebellion Québec, an environmental activist group, started climbing the bridge's structure early Tuesday morning. 0:35

Provincial police spokesperson Sgt. Claude Denis said the first 911 call came in at around 5:45 a.m. One traffic lane was closed at first. Then the rest of the bridge was closed soon after.

Police worked with the fire department to try to gain control of the situation as quickly as possible without injuries, he said.

What the arrested protesters will be charged with, if anything, was not confirmed by police. Police say the protesters will be interrogated during the day.

A protest was planned in Montreal on Monday to coincide with others across Canada and around the world, but it was postponed due to rain.

A group of more than 100 people staged a sit-in on René-Lévesque Boulevard in downtown Montreal after police interrupted their march. (Jay Turnbull/CBC)

Extinction Rebellion has been calling for protesters to block bridges and disrupt traffic. On Monday, they blocked bridges in cities such as Halifax, Toronto, Edmonton, Kitchener, Ont., Victoria and Vancouver, leading to dozens of arrests. Protests were also held around the world.

Founded in Britain last year, the movement, also known as XR, now has chapters in 50 countries.

It has other events planned for later Tuesday in Montreal.