The fire started just after 4 a.m. in the kitchen of an apartment on the fourth floor of the Châteauneuf Boulevard building, which houses a number of seniors.
When firefighters arrived, an emergency plan was triggered to help evacuate the building of occupants with reduced mobility.
The 107-unit building is constructed in concrete which, Montreal fire officials said, prevented the fire from spreading to other units.
Residents on the fourth floor won't be able to return to their units until the smoke and water is cleaned up.
The unit where the fire started was destroyed.