POLICE are calling for witnesses to a horrific crash that claimed the life of a nine-year-old girl yesterday in the state's west.

Investigators believe a truck travelling east on the Glenelg Highway at Muntham, near Casterton, left the road and rolled down an embankment about 3pm.

A 37-year-old man and a six-year-old girl were taken to the Hamilton Hospital with non-life threatening injuries while a 36-year-old woman was taken to the Royal Melbourne Hospital with serious injuries.

The nine-year-old girl died at the scene.

All four were from Murray Bridge in South Australia.

Anyone with information about the accident is urged to call Crime Stoppers on 1800 333 000.

Police are particularly interested in speaking to the owner of a car that was seen in the area at the time of the accident.