The four-alarm fire started in the basement of the residential building on Van Horne Avenue.
The flames spread quickly to the second and third floors.
No residents were harmed, but two firefighters were taken to hospital for minor injuries.
Van Horne Avenue remained closed for hours between Hudson Road and Darlington Avenue during part of the evening rush hour, causing heavy congestion in the area.
Organizations like the Red Cross and Sun Youth are now helping the families.
“Not only do they need food and clothes, but some need medication and 90 per cent of them have no home insurance,” said Sid Stevens, Sun Youth’s executive vice-president.
“If you have no home insurance and no family you can turn to, where do you go?”
Stevens said the organizations and the city of Montreal are working to help the residents find apartments.