Man sought over sex assault on NSW train

Witnesses to a sexual assault on a Sydney train have been asked to come forward as police release surveillance footage.

The 21-year-old woman was allegedly sexually assaulted on the Central to Penrith train by a man, who is about 30 years old, in the early hours of May 3.

She got off the train at Penrith, where the incident was reported to police.

Investigators would like to speak to four witnesses.

The first two are seen in CCTV images as being of Caucasian appearance and aged between 20 and 30.

One of the men was wearing a beige-coloured jacket over a white shirt and long black pants.

The other man was wearing a maroon-coloured, long-sleeve shirt and black pants.

The third witness is a man of Caucasian appearance and aged between 25 and 40 years old.

He was dressed in a black and green jacket, white shirt, and blue jeans.

The man is seen carrying a blue bag.

The fourth witness is a woman wearing black clothing.

Police said the witnesses were not involved in the attack.