Detectives from the Major Collision Investigation Unit are investigating a serious single-vehicle crash in Mount Cottrell this morning.
Investigators understand a 2004 silver Holden Commodore sedan was travelling along Davis Road when the driver veered about 12.55am.
The car flipped and rolled several times before coming to a stop on its tyres.
Emergency services responded and located a 16-year-old boy trapped in the front passenger seat.
He was removed by firefighters and transported to hospital with life-threatening injuries.
Three other occupants, a man and woman aged 19 and a 16-year-old girl, were taken to hospital with non-life-threatening injuries.
Detectives are yet to establish who was driving the vehicle at the time of the crash and have set up a crime scene while they examine the area.
Investigators are keen to speak to anyone who saw the silver Holden Commodore travelling in the area in the lead up to the crash or anyone who may have dashcam or CCTV footage.
Any witnesses or anyone with information that could assist police with their enquiries is urged to contact Crime Stoppers on 18000 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au