ACT Policing are calling for witnesses after the incident in the Monkey Bar on Bunda Street early Sunday morning.

They said a disturbance broke out among up to 20 people inside the nightclub about 2.40am.

They said a number of men and women of African appearance attempted to fight with a large group of men of Pacific Islander or Maori appearance.

Police and security guards broke up the brawl and moved the crowd outside the bar.

They said one of the men was involved in a further disturbance outside the bar before he was taken into custody.

Police are investigating both incidents and seeking the public's assistance to identify offenders.

Regional Targeting Team sergeant Jim Edwards said that in violent incidents such as these, police and licensees worked together to remove violent and aggressive patrons from licensed premises.

"Staff members have the right to feel safe in their workplace and other patrons should also be able to go out and not have their safety compromised," he said.

"Incidents such as these can wreck everyone's night and we want to identify these people to reduce the risk of them ruining your night."

Witnesses are urged to contact Crime Stoppers on 1800 333 000 or at act.crimestoppers.com.au. Information can be provided anonymously.