'Heartbroken' neighbour's heroic rescue in deadly fire

Children aged six, two and five months were killed in the fire at Lalor Park, in Sydney's west, early on Sunday after their 28-year-old father allegedly frustrated attempts to rescue them.

The father, who has not been charged, remains in hospital in an induced coma as investigators continue probing the scene for further evidence.

Four other children - aged 11, nine, seven and four - and their mother were all treated in hospital following the incident.

Neighbours and emergency services got to the fire at about 1am on Sunday and rescued two boys, aged two and six, but they died a short time later.

The body of a five-month-old girl was found inside the home after firefighters extinguished the blaze.

Neighbour Jarrod Hawkins said he acted on instinct when he realised the house was on fire after initially hearing "popping" sounds and presuming someone was trying to break into his car.

"It sounds silly, I didn't even think about it - I just sprinted straight over, kept smashing down the front door until I could get in," he told ABC TV.

"It was covered in smoke, I heard kids coughing and yelling to my right," he said.

"Not knowing where I was going, I was just on my hands and knees trying to find out where I could go."

Once he found and rescued one child, Mr Hawkins said he went straight back into the house and continued recovering others until emergency services arrived.

He is struggling to process that three children died in such tragic circumstances and the survivors left traumatised.

"I feel alright, mentally and physically, I'm just heartbroken for those kids that have to deal with that for the rest of their lives, it's just not right," Mr Hawkins said.

"They were known to a lot of people. Those kids were unreal, had great manners, very happy children, full of energy, just typical kids and unfortunately now three have lost their lives to a very serious incident."

Mr Hawkins has launched an online fundraiser for the 29-year-old mother and her surviving children, which had raised more than $17,000 by Tuesday afternoon.

Homicide detectives believe the father is responsible for the three deaths and are treating the incident as a domestic-related multiple homicide.

Attempts to enter the burning home were allegedly met with resistance.

Premier Chris Minns has foreshadowed "the most serious charges on offer" for the man, adding NSW had been "deeply wounded" by the tragedy.

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Australian Associated Press