Anti-capitalist protesters have set fire to cars and smashed the windows of banks and cafes during a rally in the Swiss city of Geneva.
Organisers, including unions and Switzerland's Green Party, broke off the march after masked protesters in the main crowd rampaged through the centre of the city.
They are protesting against a three-day World Trade Organisation conference starting on Monday, which they say works on behalf of big business and exploits the developing world.
Protesters set fire to four cars near the city bus station, causing a thick cloud of smoke.
Police used tear gas to disperse the violent protestors and no further damage was caused, a police statement said.
Police blocked off access to the WTO's lakeside headquarters, which the marchers had planned to pass.
Police blamed the violence on some 200 masked demonstrators, known as the "black bloc", out of a total crowd of 3,000.
Police arrested 17 people and seized fireworks, iron bars, bicycle chains, sprays, spanners and other objects.