Thousands of people descended on downtown Ottawa Sunday for a climate change rally that was billed as one of the largest the city had ever seen.

The 100% Possible climate march, which calls on governments to move toward 100 per cent renewable energy by 2050, was one of about 1,700 marches held worldwide on Sunday on the eve of the upcoming Paris climate change summit.

The Sunday march was organized by a consortium of environmental groups, including Ecology Ottawa and the World Wildlife Fund.

100 percent possible march ottawa gatineau

Protesters convene at Gatineau City Hall ahead of today's 100% Possible climate change march in downtown Ottawa. (Claudine Richard/ICI Radio-Canada)

"You know, this march has religious groups, it has unions, it has environmental groups, it has First Nations," said Sabrina Bowman of GreenPAC, a group that helped support candidates with environmental credentials in the October federal election, on Saturday.

"This is a real moment of galvanization."  

Marchers gathered at Ottawa City Hall at 12:30 p.m. and headed toward to Parliament Hill around 1:30 p.m.

At 4 p.m., organizers tweeted 25,000 people had participated.