A 37-year-old man, a 32-year-old woman and two of their three children are dead following an apartment fire in Les Coteaux, Que., just west of the island of Montreal.

A four-year-old girl was confirmed dead shortly after the fire, while a two-year-old boy died in hospital late Tuesday, Quebec provincial police confirmed.

The couple's other child, an eight-year-old boy, remained in hospital in critical condition.

The fire broke out in an apartment building on Des Bouleaux Street in Les Coteaux, Que., just west of Salaberry-de-Valleyfield. (Radio-Canada)

The fire began sometime around 2:30 a.m. ET Tuesday on the third floor of a small apartment building on Des Bouleaux Street, near Highway 338.

Paramedics transported all five people to hospital. They were reportedly unconscious at the time.

One neighbour reported seeing two of the children carried out of the home in their pyjama bottoms by firefighters.

"They tried to revive them, and then put them in ambulances," the neighbour said.

Four of those caught in the fire were in their bedrooms, while the fifth was in the bathroom.

Lac St-François regional fire chief Michel Pitre told Radio-Canada it appears the fire started in the living room.

"We did not find a smoke detector. Did it melt? We should have found the battery on the ground, but we didn't find anything," Pitre said.

He said it didn't take long for firefighters to put out the fire.

The investigation has been transferred to Quebec provincial police.