RICHMOND -- California Highway Patrol Officers late Monday were searching for a man they say took off running during a traffic stop with a sizable firearm in tow, authorities said.

CHP officers pulled over the vehicle about 8:20 p.m. near the intersection of 4th Street and Grove Avenue and watched as the passenger bailed from the car with a firearm in his hand, Officer Ralph Caggiano said. Officers on scene remained with the driver of the car and called in a CHP helicopter to help search for the armed passenger.

Authorities scanned the area by helicopter for about an hour before calling off the air search around 9:30 p.m. because of heavy fog, Caggiano said. Authorities believe the man may have run into one of the many unoccupied dwellings in the neighborhood, and will issue an alert to local authorities to be on the lookout for the armed suspect.

The nature of the original traffic stop was not immediately known, Caggiano said, and descriptions of the two men and their car were not immediately available.

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Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.