Officers arrived about midnight to find a group of men fighting in George Street, as bystanders looked on.

Acting Inspector Chris Breed of Sydney City Local Area Command said that about 20 people were involved.

Police arrested a 16-year-old youth and two 20-year-old males at the scene. All three were taken to Day Street police station, where they were later released pending further inquiries.

Footage supplied to Channel Nine shows punches being traded on the pavement, with the violence at times spilling out onto the road.

In one instance, a man is swung to the ground and held while another throws punches to his head, before a group of onlookers drag him away.

Witness Lachie Cumming told Channel Nine that the incident was incredibly noisy as those involved screamed and yelled; there was also the sound of smashing glasses that were reportedly being thrown.

"[There were] a few blokes throwing punches, throwing glasses," he said.

"All you kind of heard was glass shattering and punches being thrown."

At least one man was treated for minor injuries by paramedics and was taken to hospital. Police understand that he received a laceration to the back of his head.

Inspector Chris Breed said that the cause of the brawl was not yet known, but that alcohol is believed to have been a factor.

"We do understand that a number of people in that group - I'm not saying the youth - were at a licensed premises prior to the incident," he said.

He said that police had no reason at this stage to believe the fight was pre-planned.

No charges have been laid as police inquiries continue, and police are urging anyone with further information to come forward.