(ANSA) - Milan, May 1 - An undisclosed number of protesters who were caught damaging property and setting cars on fire during an anti Expo march in Milan have been arrested, police sources said Friday. Meanwhile the May Day march ended and organizers urged participants to disperse, as Milan shopkeepers and bar owners took to the streets and began sweeping broken glass and picking up trash after the devastation caused by violent elements who joined the No Expo march.Black Block anti-globalization protesters set fire to a BNL bank branch during a May Day march in Milan Friday. The protesters threw Molotov cocktails and paper bombs at police, who responded with tear gas. Clashes are ongoing in adjacent streets, with protesters throwing bottles and stones and cops lobbing tear gas in a bid to disperse them.

Milan Mayor Giuliano Pisapia said Friday violent protesters will be punished. "We must isolate, identify and punish the criminals who are devastating Milan," he said. "We fully support law enforcement as they face an urban guerrilla set off by violent imbeciles, who must end up in prison," tweeted Lombardy Governor Roberto Maroni.

A large column of smoke on Friday could be seen over a building in downtown Milan, probably caused by a paper bomb thrown by protestors against a store on the ground floor. Meanwhile the central Largo D'Ancona, between Corso Magenta and Via Carducci, was isolated after protesters set cars on fire and formed a barricade with garbage bins. Police were able to disperse part of the protesters dressed in the fashion of Black-Block anti-globalization demonstrators while others were continuing to throw objects including bottles and stones against the officers. Two plain-clothes officers were also reported to have blocked a demonstrator dressed in black, his face covered, and to have dragged him amid anti-riot police. Police officers are talking with members of the No Expo march as it was clear different groups of demonstrators were in disagreement.

A reported 100 protestors set three cars on fire Friday in Milan, as the Expo world's fair kicked off not far from the city center. Dressed in the style of the so-called Black Block anti-globalization demonstrators, the protesters threw stones and bottles at police in Milan's Corso Magenta. Police responded with tear gas, dispersing the group of youths who broke several shop windows and created a barrier with flower vases and garbage bins, isolating Largo D'Ancona off Corso Magenta in central Milan. A paper bomb was also reportedly thrown against a store. Anti Expo protesters threw objects and firecrackers at police in riot gear in Milan's Piazza Resistenza Partigiana, sources said Friday. Police responded by trying to disperse them with water cannon but protesters are not giving in.

The clashes began shortly after the No Expo march began snaking through Italy's business capital Friday, led by protesters carrying a banner with the Expo logo and the slogan "debt, cement and precariousness".

Just as the universal exposition that opened Friday is dedicated to the theme of feeding the world, so are many of the protests by the marchers using the hashtag #NoExpo.

Demonstrators began congregating in the centre of Italy's business capital earlier in the day in readiness for a big 'No Expo' protest march. Milan police authorised the march to go ahead but banned it from the Piazza Duomo cathedral square and the vicinity of Largo Cairoli, where the Expo entrance is located. Authorities are concerned that hundreds of foreign demonstrators who arrived in Milan Thursday could stage violent protests and damage the city center, police sources say. Anti-riot police have been deployed in large numbers along the march route and at strategic points in the city to prevent trouble erupting.

