St Patrick's Day is a real riot as police arrest 11 at Ontario student party

Police in Canada say they will use social networking websites to identify young vandals and bring them to justice, after a raucous St Patrick's Day celebration turned into a five-hour pitched battle.

The city of London, Ontario, was still clearing up yesterday after a crowd of about 1,000 youths fought with emergency services who had been called to the scene of a fire shortly before midnight on Saturday.

They reported being bombarded with bricks, bottles, and car tyres by drunken revellers, who were mostly students from Fanshawe College, a local university. The local police chief called it: "the worst case of civil disobedience our city has ever been subjected to."

Just 11 arrests were made on the night, but detectives said yesterday that they would use Twitter and Facebook to identify people caught on film attacking officers. Many posted videos in which they boasted of setting fires or destroying property.

Trouble started in a street dominated by student housing at around 10pm, when firemen were called to a small brush fire.

After stepping out of their engine, they were pelted with tyres, bricks, and beer bottles. The swift arrival of 60 police officers served only to escalate the violence. Cars were soon being turned over and set on fire, as flaming mattresses, pro- pane tanks, and flat-screen tele- visions fell from upstairs windows.

"To say that I am disappointed and disgusted is an understatement," said Joe Fontana, the city's Mayor.

Footage of the riot showed an crowd gathering round the embers of a smouldering truck. In a surreal moment, they began singing the Canadian national anthem: "O Canada!"

In June, thousands of ice hockey fans fought pitched battles with police in Vancouver, after the local team lost a big match.