Eight people were shot and four others injured by flying debris Sunday night when someone opened fire during a fight outside a concert in San Francisco, police said Monday.

All the victims suffered non-life-threatening injuries, police said.

The incident happened outside the Regency Ballroom at 1290 Sutter St. shortly before 10:15 p.m. Sunday.

An argument between two men escalated into a fight among four men, police said. Another man walked up to the crowd, pulled out a gun and began shooting.

Eight people were struck by gunfire, and four others were wounded by shrapnel or broken glass, authorities said. They were treated at San Francisco General Hospital and Kaiser hospitals in Vallejo and Oakland.

The gunman fled on foot. He was described as black, in his 30s, wearing an unbuttoned white shirt with pinstripes, white T-shirt, blue jeans and a baseball cap.

Police did not report any problems inside the sold-out concert, KMEL House of Soul. The program director for KMEL, Stacy Cunningham, did not return a call seeking comment.

Police detained one man after the shooting, but witnesses said he was not the gunman. He is being held on other weapons allegations.

"This was at the end of an event, and several people were around at the time and witnessed what happened," said Sgt. Wilfred Williams, a Police Department spokesman. "We are encouraging those people to come forward and help us identify the shooter."

A spokesman for the Regency Ballroom, Michael Roth, emphasized that the shooting happened in the middle of a street and that it is not known whether it was tied to the event.

Roth said the gunman "was not in the show, because he was observed outside the theater several times in the evening by our security."