GENEVA - Swiss police fired tear gas and rubber bullets on Saturday at hooded protesters who broke windows and set cars alight during a demonstration ahead of a major WTO conference in Geneva.

These are among the vehicles set on fire by anti-capitalist protesters Saturday in Geneva, Switzerland. (Dominic Favre / AP) Thousands marched in the protest ahead of the World Trade Organisation ministerial meeting beginning on Monday, with the vast majority of demonstrators not participating in the violence.

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.

Some 200 violent protesters infiltrated the march and "began to inflict damage right from the start of the demonstration," police spokesman Patrick Puhl said. Police fired tear gas and rubber bullets to stop them.

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.

One young protester dressed as a vampire told AFP he "understood people's anger as the crisis had hit them very hard" while an elderly woman said that the recent economic turmoil gave people "plenty to be angry about."

Organisers put the total number of protesters at 5,000, while police said it was 3,000.

Police spokesman Eric Grandjean told AFP 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.

Three South Koreans had been barred from entering Switzerland for the protest after being accused of violent behaviour at past demonstrations, a police spokesman said.

Dosuk Han, head of the Korean League of Small Farmers, as well as Kangsil Lee and Jejoon Ju from a campaign group for farmers, were being held at the Geneva airport on Saturday, protest organisers said in a statement.

The organisers demanded their immediate release.

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

More than a hundred ministers will gather for the WTO conference, though there have been concerns linked to the United States and European Union.

Diplomats in Geneva note that the fact that the United States still has no ambassador to the WTO is a sign President Barack Obama's administration has put little emphasis on trade talks at the moment.

Meanwhile, the European Union will lose its Trade Commissioner Catherine Ashton on the second day of the WTO ministerial, as she is due to step into her new post as foreign policy chief.

"It is true that the American administration's political calendar is currently more focused on the reform of the health system, the environment and financial regulation than on trade," WTO head Pascal Lamy told AFP.

"But nevertheless, the United States is committed to the negotiations."

As for the European Union, he noted that Development Commissioner Karel de Gucht has been proposed to replace Ashton, calling him a "solid and skillful negotiator."