SAN FRANCISCO -- A gunman opened fire at a group of fighting men, injuring 12 people outside a concert hall, authorities said Monday.

The gunfire erupted Sunday night near the Regency Ballroom after several men were involved in a fist fight, San Francisco police Sgt. Wilfred Williams said. The victims were taken to hospitals with non-life threatening injuries.

At some point, a man standing near the fighters opened fire in their direction before running away, police said.

The suspect did not appear to be related to either of the fighting parties and was not part of the fist fight, Williams said.

Eight people were shot and another four were injured by glass and bullet fragments, Williams said. The men involved in the fight, who were not identified, were not hurt.

Police said the concert had let out when the fist fight broke out. It was not immediately clear whether the men in the fight or the gunman attended the concert, which was sponsored by San Francisco hip hop and rhythm and blues station KMEL.

Police detained one man after the incident and said they found weapons in the trunk of his car, but Williams said he played no role in the shooting.

No arrests have been made in the shooting.