Twenty protesters were arrested at the scene of a climate demonstration that blocked traffic for several hours on the Bloor Viaduct on Monday, police say.

Protesters shut down the major four-lane bridge through the morning before the arrests were made.

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

"A further breakdown will be released at a later time," she said.

Some protesters who refused to walk away from the middle of the roadway were carried off by police.

Police tweeted that the roadway had reopened just before 1:30 p.m.

The climate protest completely shut down traffic on the roadway Monday, with no cars able to cross the major four-lane bridge.

Extinction Rebellion, the group behind the protest, had its members block traffic around Broadview and Danforth avenues.

Demonstrators painted the roadway on the Bloor Viaduct during the shutdown. (Mark Bochsler/CBC)

Toronto police tried to divert drivers from the area. Cyclists could still use the bridge's bike lanes, while TTC subway service was also unaffected.

Irene Alatzakis, co-lead of outreach and communities for Extinction Rebellion, said the group is organizing in 60 cities around the world to "call attention to the climate crisis.

"We have to act as if it's an emergency," she said.

The protest stretched into the early afternoon. (Mark Bochsler/CBC)

Just weeks out from the federal election, Alatzakis also had a message for the leaders of Canada's political parties.

"We're very disappointed that you're not taking the climate emergency seriously ... we're really disappointed with all political parties that we had to do this."

The group attached Extinction Rebellion's logo — a large, green hourglass-like shape — to the side of the bridge, making it visible to drivers on the Don Valley Parkway below. Marching onto the bridge, the group carried large block letter signs saying "Act now."

Global Rebellion on the Bloor Viaduct, our blockage is in place! Come join us and demand <a href="https://twitter.com/hashtag/ClimateAction?src=hash&ref_src=twsrc%5Etfw">#ClimateAction</a> <a href="https://twitter.com/hashtag/TheTimeIsNow?src=hash&ref_src=twsrc%5Etfw">#TheTimeIsNow</a> <a href="https://twitter.com/hashtag/ExtinctionRebelionToronto?src=hash&ref_src=twsrc%5Etfw">#ExtinctionRebelionToronto</a> <a href="https://twitter.com/hashtag/ExtinctionRebellion?src=hash&ref_src=twsrc%5Etfw">#ExtinctionRebellion</a> <a href="https://twitter.com/hashtag/GlobalRebellion?src=hash&ref_src=twsrc%5Etfw">#GlobalRebellion</a> <a href="https://t.co/6AG1387NCa">pic.twitter.com/6AG1387NCa</a> —@XR_Toronto

Others carried smaller, homemade signs.

"Your home is burning, we can do something," read one.

Extinction Rebellion has already targeted a bridge in Nova Scotia and plans to protest in Vancouver, too. Protests are also scheduled for London, Paris, Berlin and New York.

Dozens of protesters took part.

Last week, Toronto city council unanimously voted to declare a climate emergency, joining hundreds of other municipalities around the world who have done the same.

However, that move was not without controversy, with some pointing out the city is spending billions to rebuild the aging eastern portion of the Gardiner Expressway.