Prague experienced its worst rioting since the return of democracy yesterday when police stopped demonstrators reaching the conference hall where the IMF and World Bank were holding their annual meeting.

For the first time since the Velvet Revolution against communism, police in riot gear used water cannon, tear gas and stun grenades, in a series of vicious confrontations with militant protesters in the city's narrow streets.

Black-clad demonstrators wearing scarves round their faces and gas masks threw Molotov cocktails and cobblestones against the police lines but only small bands were able to get close to the Congress Centre. By late afternoon 51 police had been injured.

An estimated 9,000 protesters from all over Europe took part in the demonstration to protest against global capitalism and IMF and World Bank policies in developing countries. This was a much lower number than the 20,000 expected by organisers, let alone the 50,000 who protested in Seattle against the World Trade Organisation.

After several small protests over the weekend, thousands of demonstrators assembled in front of a church in Namesti Miru (Peace Square) yesterday morning and then set off on an illegal march towards the Congress Centre, 1.5km away.

The protests were meant to be peaceful and at first there was a carnival mood, with giant puppets, sound systems and marching bands.

There were colourful delegations from a kaleidoscope of European protest groups, from placard-waving Greek Socialist Workers to British peace students in pink costumes and Turkish communists waving red flags.

However, tension rose when the demonstrators reached the police line holding the strategic Nusle Bridge, the main approach road to the Congress Centre.

As police helicopters circled ahead, activists from the Italian Ya Basta! movement - in home-made foam armour, holding tyre tubes and cardboard riot shields - moved forward slowly. This spearhead was unable to force its way across the narrow bridge, leading to a stand-off.

The march acted as a diversion while hardline anarchist protesters split off to try to reach the Congress Centre through the narrow streets below the bridge. Protesters ripped up advertising hoardings, trees and litter bins to build barricades and used cobblestones, sticks and bars against the police.

During two or three hours of sporadic fighting within a few hundred metres of the Congress Centre, police at first fell back but then pushed forward using tear gas, water cannon and an armoured car to clear the streets.

Czech police are inexperienced with such demonstrations but yesterday they kept their discipline and successfully protected the IMF/ World Bank meeting. An extra 6,000 police from around the country had been drafted in to support Prague's 5,000-strong force, easily outnumbering the assorted demonstrators.

The riots occurred in a city that has been all but deserted by residents. Children have been given the week off school and many families have seized the chance to leave Prague for their country cottages.