Major Collision Investigation Unit detectives are investigating a multi-vehicle collision in Pakenham South which has sadly claimed the lives of two people.

Investigators believe a white utility collided head-on with a silver SUV on Healesville-Koo Wee Rup Rd about 8am on Thursday (Feb. 4).

The female driver of the SUV sustained life-threatening injuries and was airlifted to hospital in a critical condition.

Tragically, the 34-year-old Koo Wee Rup woman and her unborn child have since died.

Her two passengers, both young children, sustained non-life-threatening injuries and were transported to hospital as a precaution.

The male sole occupant of the utility was also airlifted to hospital and remains in a critical condition.

Investigators have been told the white utility collided with several other vehicles prior to the head-on collision, causing minor damage to those vehicles.

Police are investigating the circumstances surrounding the collision and it remains ongoing.