NSW Police say it is too early to tell what started a house fire that killed a five-month-old girl in Bargo, south-west of Sydney on Sunday night.

Emergency services were called to the home on Avon Dam Road just before 6.30pm on Sunday and arrived to discover it well alight.

Camden Police Area Command Duty Officer Chief Inspector Stephen Greer said the girl’s grandfather was the first to notice smoke coming from the baby’s room, where the fire is believed to have started.

“The baby was asleep in the bassinet at the time,” Chief Inspector Greer said.

“The grandparents tried to get to the child, but due to the smoke and fire they were unable to.

“The death of a five-month-old child, or any child, is absolutely tragic – everybody gets affected … it’s just terrible.”

The house was well alight when firefighters arrived. Photo: ABC

Four other people were in the house at the time, including an 18-month-old boy, who was taken to Campbelltown Hospital for observation.

A 79-year-old woman and a 57-year-old man were treated for smoke inhalation and lacerations, and a 27-year-old woman was treated for shock.

Chief Inspector Greer said community members did their best to help fire crews fight the blaze, which took several hours to extinguish.

“They grabbed the hoses,” he said.

“They’ve done the best they could.”

Police are investigating whether an oil heater could have been the cause of the fire.

-ABC