HOUSTON, Texas — (CNN) -- A gunman is on the run after killing two people on a Houston freeway as horrified motorists watched during evening rush hour, authorities said.
Police initially got the call of an accident at 5:55 p.m. Thursday but when they arrived seven minutes later, they found a shooting scene.
The fatal shooting started as a crash between two cars going eastbound on Interstate 10, Houston Police assistant chief Bobby Dobbins said at a news conference.
"One of the vehicles struck the other vehicle and spun it out ... similar to a pit maneuver," he said.
Gunman fired as the car rolled down the hill
Two occupants from the vehicle that hit the other came out, and one had a weapon, police said. He started firing at the vehicle they'd just hit and pursued it as it rolled down the hill, firing rounds, police said.
"At one point, the vehicle came to a stop. He got in front of the vehicle and fired rounds into the front windshield of the vehicle," Dobbins said. "Road rage? An accident? Narcotics? We just don't know yet so I won't speculate," he added. "I will say there were narcotics found in this vehicle."
Journalist describes an 'unreal scene'
Daniel Gotera, a journalist for local station KHOU-TV, said he heard the gunshots and saw people fleeing.
"Unreal scene just witnessed on I-10 in Houston," he tweeted. "A guy gets out of his car with gun just shooting in the middle of freeway. Unbelievable."
Police said one of the witnesses had a pistol in his car, and fired several rounds at the shooter when he turned toward him. While it's unclear whether the gunman was hit by gunfire, it made him run back up the hill, get in his vehicle and flee the scene, authorities said.
Witnesses provided CPR until police arrived but the unidentified occupants in the car that was struck did not make it. Houston police are urging anyone who was in the area at the time to come forward.
That part of the freeway will be closed for investigation and officers are urging motorists to use alternate routes.