Photo: vicpolicenews

Investigators have been told a female boarded the route 57 tram toward West Maribyrnong about 10.40pm on 16 February 2018.

As the tram was on Victoria Street in North Melbourne, a man stood behind her and sexually assaulted her.

It is believed another female on the tram observed the incident and called the victim over to her.

The man got off the tram at the next stop on Victoria/Errol Street and walked east along Victoria Street.

The man is perceived to be of Indian Sub-Continental appearance with a solid build, black beard and was wearing a black head covering, red t-shirt and black pants.

Investigators have released images of a man they believe may be able to assist with their enquiries.

Investigators would like to speak to the female bystander who assisted the victim.

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