Investigators looking into a deadly fire that killed a six-year-old girl and left another child fighting for their life in hospital are trying to establish whether the house had a functioning smoke alarm.

A 46-year-old woman was also killed and several other people injured when the blaze erupted in a home at St Johns Road in Heckenberg, in Sydney’s south-west, shortly after 12.30pm.

Fire and Rescue NSW Superintendent Adam Dewberry said police and firefighters had found eight people who had managed to flee the burning building.

A six-year-old girl and a 46-year-old woman were found dead after a house fire in Heckenberg. (Kate Geraghty)

Several of the residents were injured, including one man with critical burn injuries, among them airway burns.

A child had also suffered critical injuries.

They told police and firefighters there were others inside the house.

Investigators are working to establish whether the home had a smoke alarm. (Kate Geraghty)

“Despite their best efforts they were unable to enter the home due to the extreme conditions,” Dewberry said.

He said flames had been leaping from all the windows of the home.

It took firefighters about 90 minutes to fully extinguish the blaze.

Inside, emergency services found the bodies of a six-year-old girl and a 46-year-old woman.

They are yet to be formally identified.

Several other people were injured. (9News)

The critically injured child and man were also taken to hospital.

Dewberry said while little information was available as to where and how the fire started, investigators were focusing on whether there was a smoke alarm.

“At this stage no information to indicate a smoke alarm had been operating,” he said, noting the same had been established for a fatal house fire in Guildford just yesterday.

“This house has been totally gutted by the fire. An absolute tragedy here.”

Police are investigating and a report will be prepared for the coroner.

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