POLICE believe as many as four people may have witnessed a woman being raped on a train on her way home from a night out in Kings Cross.

The 21-year-old had travelled from Kings Cross to Central at 4.40am and was on her way to Penrith when she was attacked on May 3.

She was sexually assaulted by a man in his 30s before reporting the incident at Penrith station.

Investigators believed four people may have witnessed the attack and are urging them to come forward.

media_camera Police believe up to four people may have witnessed a woman being raped on a train. Picture: Police Media

The first two witnesses are depicted in CCTV images as being of Caucasian appearance and aged between 20 and 30 years old.

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

The other man was last seen wearing a maroon coloured long sleeve shirt and black pants.

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

He was last seen wearing a black and green jacket, white shirt, and blue jeans. The man is depicted carrying a blue bag.

media_camera A woman was raped on a train between Central and Penrith last month and police are appealing for witnesses. Picture: Police Media

The fourth witness is a woman last seen wearing black clothing.

Penrith Inspector Harry Goeding said police consider the attack a “serious incident”.

He said it was not unusual for the trains taking people home after a night out to the western suburbs to have many commuters on them.

Police said the witnesses were not involved in the incident.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000. Information can be given anonymously.