Three children dead, four in hospital after house fire

Police and the fire investigations unit
Police arrested a man at the scene of a deadly house fire at Lalor Park in Sydney's west (file pic). -AAP Image

Three children are dead and a man is in custody after a horrific house fire in Sydney west.

Emergency services were called to the home in Lalor Park at 1am on Sunday. 

Two boys, aged two and four, were taken to Westmead Hospital in a critical condition but died a short time later.

The body of the third child, believed to be a 10-month-old girl, was found after Fire and Rescue NSW extinguished the fire.

Four other children were treated at the scene by paramedics.

NSW Fire Rescue Superintendent Adam Dewberry said it was a confronting scene.

"Going to a house fire you are always expecting the worst and hoping it won't be - but this was pretty confronting, absolute chaos," he told Nine's Weekend Today.

A girl, nine, and three boys aged six, seven and 11 were  taken to Westmead Hospital in stable condition.

A 29-year-old woman was also taken to hospital suffering smoke inhalation.

NSW Police arrested a 28-year-old man at the scene.

He was treated for smoke inhalation and taken to hospital under police guard.

The cause of the fire is not yet known.