The incident occurred around midnight when two large groups became involved in a brawl on a wharf on Pirrama Road, Pyrmont.
Police arrived at the scene to find find an 18-year-old man with stab wounds to his buttocks.
He was treated my paramedics at the scene before being taken to St Vincent’s Hospital in a stable condition.
A crime scene has been set up and police are appealing for the public to help identify a man who may be able to help with their investigations.
He is described as being of Mediterranean/Middle Eastern appearance and aged in his mid-20s.
He was wearing a black jacket.
Anyone who may have seen the incident should contact Sydney City Police or Crime Stoppers on 1800 333 000 or https://nsw.crimestoppers.com.au.