Emeryville police Sgt. Fred Dauer said one officer suffered minor injuries while trying to break up the melee at the bar at 6702 Hollis St. and two other officers were assaulted but weren't injured.
Two people were arrested on misdemeanor charges of obstructing, resisting and delaying police officers, Dauer said.
At least one person who was involved in the brawl was injured but left the scene without seeking medical attention or help from police, he said.
Dauer said that at about 1:25 a.m., acting Emeryville Sgt. Richard Lee was flagged down by security guards at Kitty's who said there was a large fight involving patrons with knives and guns.
Officers didn't see any weapons, although they did see people brandishing bottles and broom handles, Dauer said.
Lee asked for assistance from the four other Emeryville officers who were on duty at that hour. They tried to get everyone to disperse but were unsuccessful, Dauer said.
Kitty's patrons continued to fight on the street and turned on officers who tried to come to the assistance of a man who was on the ground and was being kicked by several people, according to Dauer.
The Emeryville officers then called for assistance from officers from Oakland, Berkeley, the California Highway Patrol and University of California at Berkeley, he said.
About 30 officers from the other agencies responded and helped Emeryville police get the situation under control by 1:45 a.m., Dauer said.
He said there have been other problems at Kitty's before in which Emeryville police have also had to ask for assistance from other agencies, but the incident today "was the worst incident we've had."
Kitty's officials couldn't be reached for comment.
The bar's website says Kitty's was established in 2005 and is "the spot in the East Bay to check out the best DJ's spinning reggae, old skool funk, R'n'B, salsa timba, reggaeton, samba and more."