Photo: bay939.com.au

Transit Crime Investigation Unit detectives understand the following sexual assaults on woman have occurred over a 12 month period:

- Route 109 tram on Collins Street shortly after 5.30pm on 16 April, 2016;

- Route 96 tram on Bourke Street, near Russell Street, shortly after 1.35pm on 16 August, 2016;

- Route 1 tram on Swanston Street, near Little Bourke Street, shortly after 8.50pm on 16 March, 2017;

- Route 96 tram on Nicholson Street, near Parliament Railway Station, 5.45pm on 26 April, 2017.

In each incident the man has approached the victim and inappropriately touched them before leaving.

Police have released an image of a man who they believe may be able to assist with their investigation.

The man is perceived to be of Caucasian appearance and at least 180cm tall with a medium build, grey curly hair and glasses.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report to www.crimestoppersvic.com.au.