Geneva police on Sunday fired teargas at protesters who set fire to a vehicle and smashed windows at a United Nations agency as they vented their anger at a Group of Seven summit about to take place across the border in France.

Some 20,000 people gathered for a march that was initially peaceful but protesters later targeted what they depicted as symbols of capitalism and multilateralism, including a parked Tesla and the UN office.

Demonstrators ripped bricks from the ground to throw at police, while children cried as teargas wafted over downtown Geneva's sun-baked streets, Reuters witnesses said.

In Geneva, businesses were boarded up and hundreds of riot police were deployed in the streets amid prior concerns about violence.

Protests have been common at G7 gatherings over the years, with many demonstrators using the summits to decry capitalism, globalisation, climate change and inequality.

The June 15–17 G7 summit in Evian-les-Bains, on the shore of Lake Geneva, will bring together the leaders of France, Britain, Canada, Germany, Italy, Japan and the United States, alongside the European Union.

Demonstrations were also held across the Atlantic. 

In downtown Calgary, Canada, hundreds of protesters gathered carrying flags and placards, chanting slogans and delivering speeches. 

According to Xinhua, the demonstrators expressed concerns over war and environmental issues, and protested remarks by US President Donald Trump regarding Canadian sovereignty.

The G7 summit is scheduled to open on Tuesday in Kananaskis, a mountain village about 100 kilometers west of Calgary.

(With input from agencies)