Detectives from Major Collision Investigation Unit are currently at the scene of a fatal crash in Balliang East.
A Hyundai sedan left Geelong-Bacchus Marsh Road and struck a tree just after 2.15pm this afternoon.
Investigators believe a green and white b-double was travelling in the opposite direction to the southbound vehicle and may have flicked debris from the road into the car.
The debris may have fallen from another northbound vehicle which was in the area prior to the crash.
The female driver died at the scene while a baby which was in the car was taken to hospital with minor injuries.
Detectives are keen to speak to the truck driver or anyone who witnessed the crash or with dah cam footage.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppersvic.com.au