Placards held by demonstrators said "Stop Capitalism, No WTO", "WTO is enemy of the climate" and "We will not sell our souls to the multinationals".

"We see the WTO making policies for the big companies, not for the people," Vera Weghmann, a 24-year-old student from Germany, said.

Organisers later decided to end the demonstration due to the violence and because police prevented the march from continuing to WTO headquarters, the Swiss ATS news agency reported.

Officers had moved in after protesters broke windows at a jewellers, banks and a hotel. Vehicles parked along the march route, particularly luxury cars, were damaged, with at least four set alight, Puhl said.

Police spokesman Eric Grandjean told AFP news agency that 33 demonstrators had been arrested, including 14 Black Block members for their involvement in the riots and four others for looting items from local stores.

Next week's gathering falls on the 10th anniversary of the  ministerial meeting in Seattle, which was marked by violent street  protests.