A mother pushing a pram has lost two young children after they were hit by a four-wheel-drive in what police said was a “most confronting” accident in Sydney.

Witnesses rushed to try to save the children by flipping the vehicle at the scene in Cabramatta in Sydney’s south-west on Wednesday afternoon.

The children, aged one and five, had reportedly been in the pram while their mother was crossing the road.

Police said paramedics treated the children at the scene and they were taken to hospital in a critical condition but both died.

Acting Superintendent Timothy Calman said it was “one of the most confronting scenes” police had seen.

He said “the community involved here this afternoon was, I can only say, phenomenal”.

“We’ve had a number of motorists that actually stopped and collectively have moved the vehicle onto its side, tipped the car over in order to get one of the children from underneath the vehicle, and other bystanders have assisted with CPR,” Calman said.

The children’s 33-year-old mother was treated for minor injuries at the scene.

A 56-year-old man who was driving the car was uninjured. He was taken to hospital for mandatory testing.

NSW Police are investigating the incident.

In a separate incident in West Melbourne on Wednesday afternoon, a girl died in a four-car crash.

Emergency services arrived at the scene about 4.30pm, and police are investigating.

A male driver and a second child in the same car as the girl who died were taken to hospital in a critical condition.

Two other passengers from the car — a woman and a child — were also taken to hospital, but with non-life-threatening injuries.

Four other people from the three other cars were taken to hospital, none in a critical condition.

-with AAP