A California Highway Patrol (CHP) officer was killed along with the suspect in the shooting and two other officers were wounded during a shootout in southern California on Monday evening, police and news media reported.
A CHP dispatcher confirmed the shootout and the fatalities happened about at about 5:30 p.m. (0030 GMT) in Riverside, California, about 55 miles (86 km) east of Los Angeles just off U.S. Interstate 215.
"One of our officers succumbed to the injuries sustained," a CHP representative said on Twitter late Monday.
The conditions of the two wounded officers were not disclosed. No other official details were immediately released by the police.
Initial reports from local news media at the scene say that a CHP officer on a motorcycle made a routine traffic stop, and the suspect grabbed a rifle from the vehicle and started shooting.
The officer returned fire and called for backup from the CHP, Riverside Police and Riverside Sheriff's Office, the Riverside Press-Enterprise reported.
It was not clear if the officer making the stop was the officer killed.
Dozens of rounds were fired, according to local media, and motorists stopped in traffic fled their vehicles and ran for cover from the gun battle.
Local broadcast media showed images of CHP patrol cars and other vehicles with shot-out windows.
Several motorists were hit with flying glass shards from bullets hitting their car windows, officials said, and were treated by paramedics at the scene.
The gunman was fatally wounded and taken to a local hospital where he was pronounced dead, the newspaper reported.
Riverside Police officer Ryan Railsback told the newspaper that the motive behind the shooting was not yet known.
That will be part of a "very long" and "complex" investigation, Railsback said.
The name of the suspect was not immediately released.