A SICKENING sex attack in broad daylight has left a female Sydney commuter reeling and police hunting the suspect.

The woman’s horrific ordeal took place last month in the city’s west and police have now released CCTV stills of a man they believe will be able to assist them.

Police say that at about 2.30pm on March 15 the 30-year-old woman boarded a train at Lidcombe to travel south.

During the trip, a man boarded the train and sat opposite the woman before exposing himself and committing an “act of indecency”, while the train was between Regents Park and Birrong railway stations.

Terrified by what she saw, the woman ran away from the man and exited the train at Birrong where she alerted staff.

The horrific incident was reported to police from the Police Transport and Public Safety Command and an investigation into the attacker began.

Today, NSW Police released CCTV images of a man who “may be able to assist with inquiries”.

The man in the photos is described as being of Pacific Islander appearance, in his 30s, about 170cm to 180cm tall, with a medium build, and short dark hair, appears to be shaved on either one or both sides of his head.

He is wearing a yellow hi-vis collared shirt, and dark shorts.

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