A father and his three-year-old son who died early Wednesday in a Montreal apartment fire likely had no warning they were in danger, officials say.

"We know for sure there was no working smoke alarm in the apartment," said Louise Desrosiers of the Montreal Fire Department.

Firefighters found the man, a 28-year-old woman and a boy unconscious on the floor near the front door of their Verdun borough apartment.

The man and the boy were pronounced dead in hospital. The woman remains in critical condition. The fire broke out in the apartment's kitchen just before 3 a.m. ET.

Police confirmed the family's dog also perished in the fire.

Firefighters reported finding a smoke detector in the ruins of first-floor apartment, but it wasn't working because it didn't have batteries.

Luc Robitaille, a fire chief at the scene, said the lack of a functional warning device in the apartment was "deplorable in 2011."

"We inspected adjacent apartments with the help of firefighters on the scene and handed out three smoke detectors."

About 40 people in neighbouring apartments were forced out into the street as a precaution while firefighters worked to bring the fire under control.

Damage to the units was minimal.

Police were called in to investigate, which is standard procedure when there's a fire death, said Const. Olivier Lapointe.

The fire department plans to canvass homes in the neighbourhood to remind people about the importance of maintaining working smoke detectors.