A 31-year-old woman boarded a Sydney-bound train at Sutherland railway station between 2.50pm and 3.20pm on January 14.

During the trip, a man got on the train and sat opposite the woman before exposing himself and committing an act of indecency between Hurstville and Wolli Creek railway stations.

The woman confronted the man, who walked away and later got off the train.

The incident was reported to police from the Police Transport and Public Safety Command.

Following investigations, officers have released CCTV of a man who may be able to assist with inquiries.

The man shown in the photos is described as being of Asian appearance, in his late 30s or early 40s, about 160 to 165cm tall, with a chubby build, short spiky black hair and distinctive acne/scarring on his face.

He was wearing a white and red t-shirt, dark shorts, dark sandals, with a black backpack and white shopping bag.

Police have urged anyone with information, or anyone who knows the identity of the man, to come forward.

Information should be provided to Crime Stoppers on 1800 333 000.