A four-alarm fire has gutted a residential building in downtown Montreal Thursday, leaving 15 people at least temporarily homeless.

The first call was received around 6:04 p.m. Thursday, according to a spokesman for the Montreal fire department.

The blaze began at 1243 St. Christophe St., between St. Catherine St. E and Rene Levesque Blvd. E, and spread to an adjacent 3-storey building.

The building where the fire originated is a total loss, while the third floor of the other building was heavily damaged.

Flames enveloped the roof of the building. As of 10 p.m., the fire was under control, but not all the flames were extinguished.

The cause of the fire was unknown Thursday night.

About 125 firefighters were called in to try and douse the flames.

They were working on a rotational basis due to the cold, the spokesman said

No one was injured.