Lalor Park house fire: Three young children are killed in horror blaze - as a 28-year-old man is arrested at the scene

A man has been arrested over a house fire that killed three young children in Sydney's west.

Emergency services were called to Freeman Street in Lalor Park at 1am on Sunday following reports a home was ablaze.  

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

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

The three children are yet to be formally identified.

Four other children, including a nine-year-old girl and three boys aged eleven, seven, and six were treated at the scene and taken to Westmead Hospital in stable condition.

A 29-year-old woman has been taken to hospital for smoke inhalation.

Police arrested a 28-year-old man at the scene as part of the ongoing police investigation.

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

Police have launched in investigation into the exact circumstances that caused the fire. 

The cause of the fire is not yet known and a report will be prepared for the coroner. 

Anyone with information about the blaze is being urged to contact Crime Stoppers on 1300 333 000.