A young child has died and two other children and a woman are fighting for their lives after an alleged stabbing inside a vehicle in Australia.

Police have confirmed that all three children involved are under the age of five, and the woman found with them is in her 40s.

Emergency services rushed to the scene in the Blue Mountains shortly after 1pm on Sunday, September 20, following initial reports of the incident.

Officers attended a car located on Waratah Road at Valley Heights, near Springwood, where they discovered the deceased child alongside the three critically injured casualties.

All four individuals had been discovered inside the vehicle with what police described as stab wounds.

When emergency personnel first arrived at the location, several members of the public had already intervened and were actively rendering first aid.

NSW Ambulance paramedics then took over at the scene, treating the two young surviving children and the woman before conveying them directly to specialist medical facilities.

In an official statement, New South Wales Police said: "NSW Ambulance paramedics treated the two children and the woman at the scene before they were conveyed to Westmead Hospital and Westmead Children's Hospital."

A formal crime scene has been established on Waratah Road, with police cordons put in place while forensic and investigative work is carried out.

For those concerned about wider public safety in the area, police have confirmed that they are not currently looking for anyone else in connection with the incident.

What we do not know yet are the specific circumstances leading up to the incident or the identities of those involved, as officers have not released further details.

Investigators are asking anyone who was in the Valley Heights area at the time, or anyone with information or dashcam video, to contact local police or Crime Stoppers. I'll keep you updated as this develops.