Firefighters and police are on the scene of a fire in a densely populated residential area in Montreal's Mile End neighbourhood on Thursday.

The first alarm for the fire was sounded at around 8:40 a.m. as smoke was spotted at a three-storey building on Laurier Avenue between Saint-Urbain Street and Esplanade Avenue.

Montreal fire department (SIM) commander Robert Rousseau said the fire started on a balcony and spread to the roof of the building, which includes a commercial establishment on the main floor and residential units on the second and third floors.

Those units were evacuated and five people were taken in by the Red Cross for care.

A fifth alarm was sounded at around 9 a.m. and 150 firefighters were on the scene. "It's because of the heat, not because of the strength of the fire," said Rousseau.

Rousseau said the heat, combined with the fire, required more rotations of firefighters so they would not overheat.

"Basically, we're battling a 1,000 degree fire in a Ski-Doo suit in 40 degree weather," said Rousseau. "We escalated the alarms quickly because of the temperature."

The fire was under control by 11:30 a.m., and the operation is being demobilized slowly.