Major Collision Investigation Unit detectives are investigating a two-vehicle collision in Tuerong last night.
It is believed the driver of a Mazda hatchback was travelling along the Mornington Peninsula Freeway when they collided with another vehicle on the Nepean Highway about 9pm.
The driver of the Mazda hatchback, a 33-year-old Mt Waverley woman, sustained life-threatening injuries and was airlifted to hospital for treatment.
Her passenger, 27-year-old Bundoora man, also sustained life-threatening injuries and was taken to hospital for treatment.
The driver of the Toyota Camry, 37-year-old Oakleigh South man, sustained minor injuries and was taken to hospital for observation.
His female passenger sustained non-life-threatening injuries and was airlifted to hospital for treatment.
His male passenger sustained serious injuries and was taken to hospital for treatment.
The other two passengers sustained minor injuries and were also taken to hospital for treatment.
The exact circumstances surrounding the collision are yet to be determined and investigations remain ongoing.
Anyone who witnessed the incident or has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au
