Northern Territory Police say a man was trying to break up a brawl at the Humpty Doo Tavern when he was hit three times and knocked to the ground unconscious.

Police allege a number of patrons were involved in the fight, which broke out at about 8:30 last night at the hotel on the outskirts of Darwin .

Detective Senior Sergeant Peter Kennon says police have been sifting through evidence at the scene and speaking with a number of witnesses.

He says the victim remains in the Royal Darwin Hospital in a critical condition after having suffered serious head injuries.

"He underwent surgery this morning and he is currently in a medically induced coma, and will be for at least five days," he said.