The fire broke out around 5 a.m. and soon escalated into a four-alarm fire.
At its height about 70 firefighters were called in to contain the fire.
"We had fire coming out three windows on the second and third floor at the north side of the building, then it started coming out the windows on the west side," said Division Commander Bob O'Halloran.
All of the people living in the apartments in the building got out safely. One firefighter was taken to hospital with minor injuries.
Part of the building collapsed at one point.
The fire has disrupted streetcar service on both the 504, 505 and 506 routes. The TTC is running shuttle buses and diverting some of its streetcars.
The cause of the fire is under investigation.