A crime scene has been established as police investigate an overnight house fire in Sydney that killed a woman and schoolgirl.

Another eight people — four adults and four children — were inside but escaped the midnight blaze.

Two of them, a man and girl, are fighting for their lives in hospital.

The house in Heckenberg, in Sydney’s west, was badly damaged when the inferno erupted on Tuesday night.

After extinguishing the blaze, firefighters made a horror discovery inside the badly damaged property on St Johns Road.

“Upon entering the house, police and fire crews located a 46-year-old woman and a six-year-old girl deceased inside,” NSW Police said.

The house fire in Heckenberg in Sydney’s western suburbs on Tuesday night.

The eight others who escaped the flames were treated at the scene.

One girl was taken to Westmead Children’s Hospital and remains in a critical condition.

A man was taken to Concord Hospital in a critical condition, while a second child and a second man were taken to Liverpool Hospital.

“Officers attached to Liverpool City Police Area Command established a crime scene and commenced an investigation into the circumstances surrounding the fire,” police said.

A report will be prepared for the coroner.

-with AAP