A teenager is dead and his mother and brother remain in hospital in critical condition following a fire at an apartment building in Lawrence Heights on Monday night.

The two-alarm fire broke out at a Toronto Community Housing building in the area of Flemington and Allen roads at around 9:40 p.m.

When crews arrived on scene, firefighters forced their way into a unit on the first floor of the three-storey apartment building and removed three injured people.

One woman, who paramedics say is in her 40s, and two teenagers were rushed to hospital in critical condition.

William Hay, an investigator with the Office of the Fire Marshal, confirmed that the three victims are all members of the same family. Toronto police have since identified the victims as a mother and her two teenaged sons.

The 18-year-old son died of his injuries in hospital, while the mother and her 16-year-old son remain in hospital in critical condition, police said Tuesday evening.

“Unfortunately we have received confirmation from the hospital that one of the three occupants that we removed from tonight’s fire has succumbed to their injuries and been pronounced dead in hospital,” Toronto Fire Chief Matthew Pegg said at the scene early Tuesday morning.

“The other two occupants that have been transported to hospital, the last update I have is that they remain in critical condition, so we are still hopeful for good news there.”

Pegg offered condolences to everyone impacted by the fatal fire.

“Our sincere thoughts and prayers go out to family, friends, and all those affected by tonight’s tragic fire,” he said.

Police have not released the identity of the deceased as they are still working on next-of-kin notification.

The fire was extinguished at around 10 p.m. and the cause and origin is still under investigation.

Hay said the fire broke out in the living room of the two-bedroom apartment where the family lived.

"We will be examining that area to see what ignition sources exist within it and hopefully by doing that we will be able to determine exactly what caused the fire to ignite," he said.

"There is a very heavy layer of smoke and soot (which is) a little unusual, likely from a smoldering fire... It’s early stages at this juncture so that’s not firm."

Hay said investigators will be on scene today and possibly tomorrow.

He was unable to comment on whether the fire is believed to be suspicious.

"Everything is on the table at this juncture," Hay said. "Our investigation is very preliminary."

Tenants in the building were temporarily displaced but residents on the second and third floors have been allowed to return to their units.

One resident told CP24 that he was first alerted to the fire by a neighbour.

"I didn’t see flames, I just saw smoke," he said. "My neighbour came in and said he saw them pulling bodies out, unresponsive bodies, and they were doing CPR on the ground."

Speaking to reporters at city hall, Mayor John Tory said he has been in contact with Toronto Fire Services about the incident and discovered that the building was last inspected a few weeks ago.

"They are now going to be conducting a very thorough investigation," Tory said.

"I just wanted to express obviously my concern about that fact that there had been such a fire and my condolences to those who have lost loved ones or who... are still in hospital."