Firefighters were dispatched to the scene on Assiniboine Road just before 4:30 p.m. ET.
Tony Bellavance, a platoon chief with Toronto Fire's north command, said that firefighters could see black smoke rising from the burning townhome as soon as they left a nearby station.
"They knew they had a fire and called a second alarm right away," he told CBC News in an interview on Monday evening.
Bellavance said the fire "was already breaking through the roof" when firefighters got to the scene.
Photos of the fire that were posted on Twitter showed flames and smoke coming out of the townhouse.
Bellavance said wind helped push the flames toward an adjacent unit, which shares a common roof with the townhouse where the fire started.
"There's two units there, they’re a semi and it looks like it broke through the roof at the rear of the building and then the wind just took it right across," he said.
Bellavance said there were people in both units when the fire broke out.
The fire was out by the early evening, but firefighters remained at the scene battling hotspots.
The CBC's Natalie Kalata reported that no one was hurt in the fire and the home was evacuated safely.
The cause of the fire is not yet known. Bellavance said the fire is believed to have started on the third floor.
Kalata reported that the damage from the fire is estimated at more than $500,000. The fire marshal is now investigating.
Megan Bronson got a phonecall about the fire and soon learned that her third-floor bedroom had burned.
On Monday evening, Bronson admitted she was still in shock to learn that "literally everything" she owned had disappeared in the fire.
York University sent a statement to media indicating that it would provide "short term housing and support tonight and longer term accommodation for students who are directly affected by the fire."
According to the school's website, York is the country’s third-largest university with a population of 55,000 students and 7,000 faculty and staff.