A man's ear has been severed during a road rage incident in Parklea on Wednesday.
Police said the man also suffered stab wounds and a head injury, and is in a critical condition in hospital.
Another man from the same car was treated for a leg injury following the incident, which began in Parklea and ended on the Stanhope Parkway at Stanhope Gardens, about 9pm.
Both men were travelling in a Toyota Hilux, while two other men from a Subaru WRX have been treated for non-life-threatening injuries and are being questioned by police.
A second crime scene has been established at Bather Street, The Ponds, where the Toyota was driven after the incident.
The Subaru was located in Rochdale Circuit, Stanhope Gardens.
Two men from this vehicle are being treated at Blacktown Hospital for non-life-threatening injuries, and assisting police with their inquiries.
Police are urging anyone with information to call Crime Stoppers on 1800 333 000.