NSW Police alleged on Monday that the SUV was stolen a short time before the collision at 7am.

Police say the owner of the vehicle had been changing its tyre on Monday morning when he was approached by a man.

Following an altercation the man managed to get into the vehicle and drive away.

Superintendent Rohan Cramsie said of the dash camera footage that it had been "extremely confronting" to view.

"I can only start to begin to imagine what the other drivers would have witnessed and experienced when they saw that vehicle coming towards them which, what we would allege, would be above the speed limit," he said.

"It's horrifying to watch."

The northbound traffic was brought to a standstill after the SUV flipped onto its roof and exploded. Several other cars, including a Honda CRV and a van were also hit.

Lanes five and six near Circular Quay were quickly engulfed in black smoke after the black Toyota Kluger caught fire.

Three people were injured as bystanders rushed the to help of trapped drivers.

NSW Ambulance Inspector Giles Buchanan described those who aided the drivers in escaping as "absolute heroes", adding "we can't thank them enough".

Superintendent Cramsie said on Monday that the driver of the Toyota was believed to be aged in his 30s.

He is now under police guard at Royal North Shore Hospital as investigators wait to question him.

It's understood he suffered serious, non-life threatening injuries.

The driver of the van, believed to be a man in his 20s, suffered injuries to the pelvis after he was trapped in his vehicle. He has been taken to St Vincent's Hospital in a serious but stable condition.

The third driver, a woman believed to be in her 60s, suffered minor injuries and has been taken to Royal Prince Alfred Hospital.