A man has been charged after two family members were killed in a crash with an allegedly stolen car in Sydney’s south-west.

Police say the man behind the wheel was driving in “one of the most extreme and dangerous” manners when the deadly collision occurred just after 11am yesterday.

Assistant Commissioner Brett McFadden alleged it started when a 31-year-old man, known to authorities, punched a 25-year-old man at a service station on King Georges Road in South Hurstville at around 10.20am.

Two family members have been killed in a crash with an allegedly stolen car that police say was driving in “one of the most extreme and dangerous” manner in Sydney’s south-west. (Nine)

He then allegedly stole the keys to the man’s red sedan from his pocket and fled the scene.

Police found the car driving on King Georges Road in Beverly Hills.

McFadden alleged the car failed to stop and a chase began with the help of a nearby police helicopter.

The chase continued along the M5 but was stopped near Bankstown. The helicopter continued to track the driver over the next 40 minutes.

“[It was] one of the most extreme and dangerous pieces of driving I’ve seen in a long time,” McFadden said.

“He was overtaking vehicles at speed, breakdown lanes, he was crossing onto the incorrect side of the road, all of which without police vehicles around him or proximate to him.”

About 11.10am, the allegedly stolen car crashed into an Alfa Romeo on the Old Hume Highway in Camden South.

The allegedly stolen car crashed into an Alfa Romeo on the Old Hume Highway in Camden South. (Nine)

Two women inside the car, aged 60 and 84, died at the scene.

McFadden said the women were part of the extended family and offered his condolences to their loved ones.

“They must be going through the absolute most tragic set of circumstances, absolutely devastating for that family,” he said.

NSW Police Assistant Commissioner Brett McFadden. (Nine)

McFadden defended the officers’ actions and said they were nowhere near the car when it crashed.

“I’ve watched the footage from our aviation support aircraft. I can tell you that there were no police vehicles around this driver,” he said.

The 31-year-old man allegedly fled the scene on foot but was arrested at gunpoint.

He was taken to Campbelltown Hospital for mandatory testing and was then taken to Campbelltown Police Station.

The man has now been charged with 11 offences, including two counts of dangerous driving causing death, two counts of aggravated dangerous driving causing death, and failing to stop after a vehicle impact that caused death.

He was refused bail and will appear in court today.

Police have set up several crime scenes and the investigation will be reviewed by the Professional Standards Command and overseen by the independent Law Enforcement Conduct Commission.

Anyone with information or footage of the incident is urged to contact police.