Police say the female patron claimed she was sexually assaulted by an unknown man on Friday night about 9.30pm, during a set from band The Jungle Giants.

The young victim was provided with assistance on the night, and Bellerive Criminal Investigation Branch has commenced an investigation into the incident.

Police and event organisers have condemned the behaviour and are urging those partaking in activities within the mosh pit to stay with friends.

Tasmania Police would like to hear from any person who may have witnessed the incident and in particular would like to speak with two female patrons who assisted the victim exit the mosh pit on Friday night.

Information can be provided directly to police at the event or via the general police assistance line, 131 444. 

Information can also be provided anonymously by calling Crime Stoppers on 1800 333 000 or online at crimestopperstas.com.au