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Police are treating the deaths of three young children in a house fire in Sydney's west as a "domestic-related homicide".
At least 20 firefighters and six fire trucks rushed to Freeman Street at Lalor Park about 1am today to find the home well alight.
Police will allege that upon arrival they encountered a 28-year-old man who "frustrated" first responders' attempts to get inside the property.
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Superintendent Danny Doherty from the NSW Police Homicide Squad alleged the man acted with "the intention of keeping the kids inside the premises".
"We're treating this as a domestic-related multiple homicide," he told reporters.
"The 28-year-old man is currently under police guard in hospital in an induced coma."
Acting Superintendent Jason Pietruszka praised the heroic actions of officers and a neighbour who went to extraordinary measures to gain entry to the home.
"Police approached, and a neighbour," Pietruszka said.
"They then had to bring the offender under arrest, they suffered various injuries as a result and that was done so in a manner that was quite extraordinary.
"The neighbour that did try to assist helped further lives from being lost."
Despite the best efforts of police and paramedics two boys, aged two and four, died from their injuries.
After firefighters extinguished the blaze, they located the body of a 10-month-old girl.
A nine-year-old girl and three boys aged 11, seven and six were treated at the scene before being taken to hospital in stable condition.
A 29-year-old woman was transported to hospital for smoke inhalation.
It's understood the man arrested at the scene was not previously known to police and had no existing apprehended violence order against him.
Fire and Rescue NSW Superintendent Adam Dewberry praised the work of first responders for what was a confronting scene.
"Just sitting there watching a little child sitting on a police constable's lap, or she's comforting him while paramedics are providing treatment," he said.
"Firefighters are handing out our Care Bears, our little teddy bears, to try and give them that little bit of comfort."
An investigation is underway into the circumstances behind the blaze, police said.
A report will be prepared for the coroner.
Support is available from the National Sexual Assault, Domestic Family Violence Counselling Service at 1800RESPECT (1800 737 732).
