A woman suffered facial injuries after she was punched by an unknown man in an inner-city nightclub on Sunday.
The woman was left nursing a swollen cheek and eye following the unprovoked assault inside the Suburbia bar on Sunday, about 2.30am.
''She is struggling to understand why it happened,'' Detective Graeme Smaill, of Dunedin CIB, said.
The victim was assaulted on the stairs leading towards the dance floor.
''According to the victim and another witness, it was just out of the blue, nothing had happened ... there was absolutely no reason for it.''
Footage taken inside the venue and CCTV footage near the Stuart St bar would be reviewed, he said.
Police also wanted to hear from patrons inside the venue at the time of the incident and who may have witnessed the assault.
Anyone with information which might assist in identifying the alleged offender should call Detective Graeme Smaill, on (03) 471-4800, or anonymously via Crimestoppers on 0800 555111.