Sainte-Thérèse, Que., resident Jacques Lauzon says he woke up shortly before 7 a.m. on Saturday to the smell of smoke.

He said that's when he ran next door and saw thick smoke coming through the window of a family's apartment in a four-unit complex at 83 St-Charles St.

Lauzon said his wife called 911 and he broke a window to get inside. He said he carried one of the children, a 3-year-old girl, out of the home.

The girl was covered in soot and barely breathing, according to Lauzon.

When firefighters arrived on the scene, Lauzon said they gave him an oxygen tank for the girl. But the neighbour says it took three tanks to finally get a working apparatus.

Police said they could not confirm whether there were problems with the emergency equipment.

3 children suffer from smoke inhalation

Firefighters reported all five members of the family were found unconscious when they arrived on the scene.

The two boys, aged 10 and 7, were rushed to Sainte-Justine Hospital for smoke inhalation. The 3-year-old girl was originally reported as stable, but later on Saturday authorities said her condition had become critical.

The father, who police say suffered burns to the upper part of his body, was taken to the burn unit at Hôtel-Dieu in Montreal.

The mother was also treated in hospital, but police said she is not facing life-threatening injuries.

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Firefighters had the apartment fire under control by 8:10 a.m. on Saturday. (CBC)

Authorities said three police officers were also treated for smoke inhalation.

The fire was under control within an hour of the 911 call.

Following the investigation by the Thérèse-De Blainville regional police and the Sainte-Thérèse fire department, authorities confirmed the fire was accidental.

Officials say the fire began in the living room fireplace. They said there was no working smoke detector in the home.