The blaze began after 7 p.m. at a home at 181 Osler St. near Davenport Road, and neighbouring homes were evacuated. One person was sent to hospital for smoke inhalation.
At the fire's height, 70 firefighters and 18 trucks battled the flames.
Neighbour Jeff Estrella saw the blaze from across the street.
"We saw black smoke coming out of the basement of that house right there, and I just ran into the house and said, 'Call 911 quick.' I was running to door to door," he told CBC News.
The house next door, at 183 Osler St., went up in smoke.
Leo Faita, who grew up in the home and came to see what remained on Monday, said his parents got out safely.
"We moved here in 1972 … I was ten years old," he told CBC News.
Faita's brother in law, Frank Cosentino, also came to see what could be salvaged from the house.
"They're old people, they lost everything," he told CBC News. "When you're young and you lose everything, there's still a future."
Cause of fire unknown
CBC News reporter Linda Ward said at least three row houses were damaged as the fire spread to adjacent homes.
The cause of the fire is unknown at this time.
Division Cmdr. Bob O'Hallarn of Toronto Fire said the flames had moved into the attic.
“One of the big challenges is the fact that once it gets into the attic … there’s only a fire stop every five houses,” he said
Firefighters are not speculating about the cause of the fire, but say the Fire Marshal's office will likely investigate due to the extent of the damage.
Firefighters say there was a fire at the same home two weeks ago.
They do not consider the fire to be suspicious.