Major Collision Investigation Unit detectives are investigating a fatal collision in Heidelberg Heights around 5.30pm tonight.
It is believed a blue Mazda turned onto Bell Street from Upper Heidelberg Road, driving onto the wrong side of the road and colliding head-on with a white Toyota.
A third vehicle was also involved. The single occupant was not injured.
The male driver and female passenger of the white Toyota were taken to hospital with non-life threatening injuries.
The male driver and female passenger of the blue Mazda were taken to hospital in a critical condition, the yet to be formally identified woman has died in hospital.
The cause of the collision is being investigated and anyone with information is urged to contact Crime Stoppers on 1800 333 000.