Rioters fought with firefighters and police in the Canadian city of London, Ontario, as St Patrick’s Day parties spiralled out of control overnight.
Dozens of police were drafted in to deal with the unrest, which was sparked when several student parties spilled on to the streets.
Rioters hurled bottles at police and set a TV truck alight, feeding the flames with a propane tank and TV sets.
Police said 11 people were arrested and appealed for rioters to come forward.
Police were called out late on Saturday, but did not move in until 04:00 on Sunday (08:00 GMT).
“Never in my 32 years as a police officer have I observed behaviours that escalated to the point where there was risk that individuals could seriously be hurt or quite frankly killed,” said London’s police chief, Brad Duncan.
“We will not tolerate this lack of respect for our community, our laws and specifically this neighbourhood.”
The authorities estimated that the damage would cost $100,000 (Ã‚Â£65,000) to repair.