A man is in critical condition after being pulled from an apartment fire in Toronto's west end on Wednesday evening.

The fire broke out in a unit on the 14th floor of a building in the area of Lansdowne Avenue and Dupont Street shortly before 6:30 p.m.

Toronto Fire platoon chief Armando Schiarizza said crews encountered heavy smoke when they arrived.

"They did have trouble finding the fire. It was a relatively small fire, but there was a lot of heavy smoke in the unit," Schiarizza said.

Firefighters conducted a primary search of the unit and located a man without vital signs. "There was some delay in having to find the individual because he was within the unit in heavy smoke," Schiarriza said.

The man was subsequently taken to a trauma centre with life-threatening injuries.

Schiarriza said the fire was knocked down quickly. He added that the blaze was isolated in that one unit.

The cause and origin of the fire are unknown.

"At this point, we have not found anything that was nefarious. But once again, we'll leave that up to the investigator to determine," Schiarriza said.