Geneva police today fired teargas at protesters who set fire to a Tesla vehicle and smashed windows at a United Nations agency as they vented their anger at a G7 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 the 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.  

Elsewhere on the march route, the wooden barriers at a Banque du Leman were ripped down and the windows smashed. 

By the end of the afternoon, Alexandre Brahier, a spokesman for the Geneva Police, said protesters were ordered to disperse after several incidents. 

Among the crowd was a group of youths wearing black hoodies and masks who gathered behind an anti-Trump banner. Signs reading 'Antisemitic never; anti-Zionist always' could also be seen.

Organisers of the protest printed a handbook for demonstrators that included a map of the security perimeter, tips on how to gear up for the march, and advice on how to behave if detained by police.

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

Demonstrators said they came to protest against the G7 as a symbol of concentrated political and economic power. 

Last week Tesla owner Elon Musk, who has worked as an advisor to US President Donald Trump, became the world's first trillionaire.

'To me, it's a meeting of the rich that shows once again how the rich can become even richer while the poor are left behind,' said protester Pippa Saugy.

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

Wars in the Middle East and Ukraine are set to dominate the agenda, while leaders will seek to avoid a clash with Trump as he seeks to finalise a framework peace deal with Iran.

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

Swiss and French authorities have deployed thousands of police to provide security for the three-day summit. 

Authorities have blocked off roads, banned unauthorized gatherings and pledged financial support for businesses who could be hit by unrest. 

Scores of businesses and shops have boarded up their storefronts with wooden panels as a precaution - wary of upheaval that left a trail of damage in Geneva during a similar summit in Evian in 2003. Only seven of the 35 roadway border crossings will remain open.

Demonstrators have been gathering for days in advance of Sunday's march in Geneva, the largest city in the area and designated gathering spot for activists who oppose the G7.

Mattia Piccard bristled at the strong police presence.

'This is an attempt to frighten demonstrators, to frighten people and discourage them from coming out to protest,' Piccard said.

Clélia Colin, another demonstrator, said she wanted to raise the issue of gender inequality.

'The values represented by the G7 are completely misogynistic, and they contribute to inequality,' said Colin.