The smoke detectors in the home where two young sisters were killed in a fire this week weren't functioning, fire investigators in Surrey, B.C., have found.

Five-year-old Sajel Saroya and her three-year-old sister Priya died early Tuesday morning after a fire tore through their north-end home.

Surrey Deputy Fire Chief Jon Caviglia told reporters at a press conference Friday that two hard-wired smoke detectors in the basement and on the first floor of the home weren't working properly, and that may have delayed evacuation of the house.

Investigators have determined that the fire was accidental, but still don't know for certain what sparked the blaze. They have yet to speak with the girls' parents, who are said to be devastated by their loss.

Nine people were inside the house when the fire broke out. Neighbours described a horrifying scene at the fire: two frantic parents on the roof and their little girls still inside the burning home.

Despite what police have described as the "heroic" efforts of neighbours to get everyone out safely, little Sajel and Priya could not be saved.

When firefighters arrived on scene, they were pushed back by the searing heat. One firefighter suffered burns to 30 per cent of his body.

He was one of six people taken to hospital with injuries. Five of those people have now been released, and Caviglia says the firefighter is expected to make a full recovery.

With files from CTV British Columbia's Lisa Rossington