The fire broke out just after midnight on the third floor of the multi-storey building at 150 Mississauga Valley Blvd.
Residents told CBC they had to exit the building through thick smoke in darkened stairwells. Eight people were taken to hospital, most suffering smoke inhalation. A handful of others were treated for minor injuries.
"An alarm sounded lights went off,” one resident told CBC News. “Someone knocked on my door. I could smell the smoke.”
By 7 a.m., many residents, including children, were seen sleeping on the lawn of a park across the street from the building. One man fled wearing only his boxer shorts.
The Red Cross was on the scene distributing food and water. City busses were also called in to provide an air conditioned environment for residents.
CBC’s Trevor Dunn was at the scene early Friday and said residents were unsure when they would be allowed back inside.
Meanwhile they were waiting outside, some trying to sleep, temperatures pushed past the 30 C mark
"Everybody got out safe but the big question is when they will get back in," Dunn reported.
Dunn said some residents believe fire may have been related to the building's air conditioning system. An ongoing heat wave in southern Ontario has taxed air conditioners and the electrical grid.