Firefighters responded at about 3:45 a.m. Thursday to 50 Rue Robinson, near the intersection of Maloney Boulevard and Rue Bellehumeur.
Flames were seen shooting from the windows of the apartment building when firefighters arrived.
Soon after, they began attacking the fire and used ladders to help rescue tenants from upstairs apartments, including Bruno Grenon, who said he woke up to smoke in his apartment.
"I checked to see where it was coming from, I noticed it was coming from the apartment below," Grenon said.
"I woke up my two roommates and I tried opening the door to the apartment, but I noticed there was too much smoke for me to get out. So I blocked the door and I started banging like crazy on the window, yelling that we were stuck up there."
Three people were taken to hospital with unknown injuries and one woman has died, police said.
The Canadian Red Cross was on site helping the more than 20 people who will be homeless for at least the next three days.
Rue Robinson remains closed to traffic.