Two children die after being hit by car in Cabramatta pram

Two children have died after being struck by a car while sitting in a pram in Sydney's south-west on Wednesday.

Emergency services worked on the children, both aged under five, at the scene at the intersection of Joseph and Gilbert Street in Cabramatta before they were taken to hospital in a critical condition.

They have since died and are yet to be formally identified.

A 33-year-old woman who police believe to be the children's mother was treated for minor injuries.

The driver of the vehicle, a 56-year-old man, was uninjured. He was arrested and taken to hospital for mandatory testing.

NSW Police Superintendent Tim Calman commended the "phenomenal" members of the public who provided assistance at the scene.

"We've had a number of motorists that have actually stopped and collectively have moved the vehicle onto its side, tipped it over in order to get one of the children from underneath the vehicle," he said.

"It's tragic circumstances for the family."

A crime scene has been established and investigations into the incident are continuing.

Cumberland Highway is closed southbound in Cabramatta between John Street and Cabramatta Road West.

A report will be prepared for the coroner.