A visually impaired woman was allegedly indecently assaulted by a man who is believed to have followed her from a railway station, onto two trains and throughout her hour-long journey across the city.

The man is accused of repeatedly touching the 23-year-old woman, who walked with the assistance of a cane, on the breast during her trip on public transport from Ashfield to Gymea this month.

While the woman's visual impairment meant she could not provide a description of her attacker to police, officers were able to examine CCTV footage from railway stations and have released footage of a man they would like to speak to over the attack on July 17.

The woman told police that she was in an elevator at Ashfield railway station between 11am and midday when someone touched her on the breast.