A man followed a 23-year-old woman from an eastern suburbs bus stop before sexually assaulting her and exposing himself.

The woman was sitting at a Doncaster East bus stop just before 9am on Monday, January 27, when a man she did not know sat beside her.

The woman walked away and was followed by the man, who attacked her before walking down a street off Blackburn Road.

Police will today conduct an operation on local bus routes to search for clues to identify the perpetrator.