Law officers were searching for a gunman early Friday after shooting erupted outside a suburban Denver concert that left three people wounded, authorities said.

Red Rocks Amphitheater was shut down after the shooting in the parking lot about 10:30 p.m. Thursday as the concert was ending, Jefferson County Sheriff's spokesman Mark Techmeyer said.

The three wounded traveled by car into nearby Denver where they were located by police and taken to a hospital.

Techmeyer said the gunshot wounds did not appear to be life-threatening, but he had no other information on the injured.

He said authorities were looking for a black male with a rifle.

Thousands of people were at the concert and all cars were searched as they left.

"Each vehicle is being checked to make sure that the suspect wasn't trying to smuggle himself out of the park," Techmeyer told The Associated Press.

No arrests had been made as early Friday.

Techmeyer said investigators were talking to witnesses and trying to determine what touched off the shooting.

The Denver Post said Nas, Schoolboy Q and Flying Lotus performed at Red Rocks, a well-known concert venue where the audience sits in an outdoor amphitheater.