Laval firefighters received a call about a fire on Ampère Avenue at 4:40 a.m. Wednesday.
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About 30 people had already been forced to leave 11 units when the firefighters arrived.
“The flames were coming from the third floor and protruding out of the roof,” said Laval firefighter spokesperson Christian Grand-Maison.
“The investigation was handed over to the police as we found two separate spots where the fire may have started.”
Thirty-five firefighters battled the flames. The fire was put out around 7:15 a.m.
Electricity was temporarily cut for approximately 100 residences in the area as firefighters fought the blaze.
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Grand-Maison said the third floor of the building is a complete loss, with damaged estimated at up to $450,000.
Nobody was injured in the fire.