Police are hunting for a man involved in an assault in Melbourne's west and have issued a public appeal for assistance in identifying the man.

Police investigators have been told a 19-year-old woman was walking north along Bulmans Road, Melton West, around 10pm last night when a car pulled up behind her.

According to the victim's statement, the male driver asked her if she wanted a lift but she refused.

The driver then got out of the car, grabbed her by the hair and punched her in the face, causing minor bruising.

A car was driving towards the pair at the time of the incident and the man then released the girl, got back in his car and drove off north along Bulmans Road.

The man is Caucasian and possibly a heavy smoker.

Melton Crime Investigation Unit detectives are keen to speak to any witnesses, in particular the driver of the other car that was in the area at the time.

Police do not have a description of the man or his car. Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppers.com.au.