Two people were taken to hospital early Monday after a fire in a 20th-floor unit at a highrise residential building in the north end of the city.

Emergency responders were called to a building on Forest Laneway, in the Yonge Street and Sheppard Avenue area, shortly before 6:15 a.m.

Firefighters quickly knocked down the blaze, which was contained to the unit, Fire Chief Matthew Pegg told reporters at the scene. There was minor smoke damage to other units, as well as the hallway, he said.

Three people required treatment by paramedics. One was transported to hospital in serious condition, while another was transported in life-threatening condition, according to Toronto Paramedic Services.

Paramedics initially said the third patient was not transported to hospital. Pegg later updated that to say the third patient, the building's superintendent, was taken to hospital to be treated for smoke inhalation. He was in stable condition.

The nature of the other victims' injuries was not clear.

Investigators are working to determine the fire's cause and origin. Toronto Fire inspects highrise buildings once a year, Pegg said, and this one had been inspected in January. It was found to be in compliance with the fire code, he said.