A riot broke out and an officer was wounded in a neighborhood of Montreal where a young man had been shot and killed by police.
Several hundred police officers fanned out trying to track down an undetermined number of youths who began setting fires in the neighborhood late Sunday before running off.
Fire trucks arriving to fight the blazes in the borough of Montreal North were pelted with beer bottles, while bus shelters were trashed. People of all ages were seen looting computers, TVs and other items from stores.
Montreal police spokesman Ian Lafreniere said two police officers and an ambulance technician suffered non-life threatening injuries. One of the officers was shot in the leg. The ambulance technician was hit in the head by a Molotov cocktail that did not ignite.
Police had made some arrests by 3 a.m. Monday (0800 GMT) but were unable to give many details.
Montreal North is a multiethnic borough where tensions between residents and police have simmered in the past.
"There's definitely a problem," said borough Mayor Marcel Parent. "We've got to fix this."
The catalyst for the violence was the shooting by police on Saturday night of three people, including an 18-year-old man who died. The man, identified by his sister as Freddy Alberto Villanueva, died from his wounds in hospital.
The other two, an 18- and a 20-year-old, were listed in stable condition.
Montreal police said the officers were trying to arrest an individual in Henri Bourassa Park when they were surrounded by a group of about 20 youths.
A few individuals allegedly broke away from the group and rushed the officers.
According to police, one of the officers then opened fire.
The officers were not wounded.
Quebec provincial police have taken over the investigation into the shootings.
"We do think there are many witnesses, because at that time ... there were a lot of people in the park or in the surroundings of the park," said Quebec provincial police spokesman Gregory Gomez del Prado.
"There were also people who were part of the altercation, and many people playing sports or just sitting in the park," he said. "It's too early to say what happened exactly. We're talking about the death of a man. It's a major investigation."
Villanueva's sister, Julissa, said from nearby Laval that family members want answers.
"We only know what we see in the news, in the newspapers, that's all," she said, breaking into tears as she spoke about her brother, a student who wanted to become a mechanic.