"Due to the large number of CCTV cameras in the Square and others operated by businesses in the area, we have some clear footage of events leading up to and after this assault.
"Police want to identify the man who was wearing a blue hoodie and maroon pants, and in one shot is riding what has been described as a silver/grey mountain bike.
"We appeal to any one that may have been around that area at the time and saw a person matching this description to contact police."
The man is described as Caucasian, in his early 20s, and of skinny build. He had shoulder-length dark hair that was dirty and unkempt.
The crime will be featured on Police Ten-7 tomorrow night in a bid to help identify the man.
Anyone with information is asked to contact Detective Oram on (06) 351 3877, or anonymously contact Crimestoppers on 0800 555 111.
* Police Ten-7 airs on TV2 at 7.30pm on Thursday.