An 18-year-old girl was assaulted in one of the female toilets at Jubilee Park late last night.
The incident occurred between 11.30pm-12am and left the victim shaken and with a minor injury.
The woman managed to fight off the offender who was described as Maori in his 40s with a distinctive thick beard that came down to his chest, bushy eyebrows and of a large build.
After fighting him off, the offender ran away and the teenager immediately called Police who scoured the area but could not locate the man.
Detective Senior Sergeant Craig Johnston says police believe the attack was sexually motivated.
Police would like to hear from anyone who was in the Gladstone Road area between 11.30pm-12am last night or anyone who believes they know who this man might be.
Information can be reported to Nelson Police Station on (03) 546 3840 or anonymously to Crimestoppers on 0800 555 111.