Woman and child dead after 'horrific' house fire at Heckenberg in ...

A woman and child have died and another two people are in a critical condition after a "horrific" house fire in Sydney's west overnight.

Emergency services were called to St Johns Road at Heckenberg at 12:40am on Wednesday to reports of a fire.

A 46-year-old woman and a six-year-old girl were found dead inside the home, NSW Police said.

Police said eight other people, including four children and four adults, who were inside the home at the time, escaped.

All occupants were treated at the scene by paramedics.

NSW Fire and Rescue said crews managed to control the house fire, which was well involved, within an hour and a half.

A girl was taken to Westmead Children's Hospital and a man was taken to Concord Hospital in a critical condition.

Police said a second child and man were taken to Liverpool Hospital.

Fire and Rescue NSW Superintendent Adam Dewberry said the fire was "horrific and confronting" and was "coming out of every window".

He said there was no indication about what caused the fire, or that the home had working smoke alarms.

"Police forensics are starting to work their way through this tragic scene to have a look at where and how this fire actually started," Superintendent Dewberry said.

Fire and Rescue NSW Commissioner Jeremy Fewtrell said firefighters had tried but failed to access the home through a window, due to the intensity of the fire.

Commissioner Fewtrell said fire investigators had partially examined the scene and were now focusing on the rear part of the property.

"I'd just like to commend the efforts of firefighters. They were confronted with a very challenging scene," he said.

"They've been able to partially get through the examination of the scene, they've still got a fair bit to go … At this stage it's still too early to say what may have caused the fire."

Neighbour describes 'frightening experience'

Neighbour Lucia Swainston said she heard an explosion just before 12:30am and saw the fire spread throughout the house quickly.

She said she went to the home to offer help and noticed people escaping from the inferno with burns and injuries.

"I noticed someone running from outside the gate of hers and it appeared he had burns and he was cut or had some wounds or something on his hand," she said.

"It was a frightening experience and then it was engulfed in flames. It went from the kitchen to the rest on the house in seconds."

Superintendent Dewberry urged people to check their smoke alarms to make sure they were working.

"It doesn't matter what starts the fire but we do know working smoke alarms save lives," he said.

"Smoke alarms are that first line of defence for you to protect yourself, your family and your loved ones."