An investigation is underway following reports of a carjacking after a crash at Arncliffe last night.
Police have been told that just before 12.30am on Saturday, two cars - a Mazda and Range Rover - were involved in a collision in the M5 tunnel near the intersection of Marsh Street.
The Range Rover was shunted out of control, then flipped and landed on its roof, injuring the 19-year-old female driver.
Two male occupants from a Honda - which was not involved in the crash - stopped to offer assistance.
The two men were rewarded for their concern with a carjacking by the occupants of the Mazda involved in the incident.
It's reported five men from the Mazda threatened the driver of the Honda with a knife, before driving away towards Marsh Street.
The men then drove off in the 2009 black Honda Accord with a NSW number plate, police said.
The 19-year-old woman was taken to St George Hospital in a stable condition with cuts, bruises and a suspected broken hand.
NSW Ambulance acting Inspector Paul Sweetland said it was "quite amazing" the woman had not suffered more severe injuries.
Investigators are appealing for anyone who sees a black Honda Accord sedan with NSW registration 'EDB35X' to not approach the occupants, but to contact Triple Zero or Crime Stoppers.
