A manhunt was launched by police in the California city of El Cajon on Thursday after a shooting at a dentist's office left one dead and two injured, local media reported.
Police in the town, about 20 miles (30 kilometers) outside of San Diego, said on social media they were searching for an "armed and dangerous" 29-year-old suspect who fled the scene after the attack, which they described as "an active shooter event."
The two people who were injured were taken to the hospital in stable condition, local TV station KUSI reported.
It was unclear whether the shooter knew the victims.
Gun violence is common in the United States, where there are more guns than people and about a third of adults own a firearm.
Polls show a majority of Americans favor stricter gun regulations in theory, but the powerful firearms lobby and mobilized voters supporting the country's culture of strong gun rights have repeatedly made congressional action politically difficult.
A divided US Supreme Court heard arguments on Wednesday on the legality of "bump stocks," simple devices that can allow rapid fire from otherwise semi-automatic guns.
That case stems from the worst mass shooting in US history, in October 2017, when a man fired on a crowd attending an outdoor music concert in Las Vegas, killing 58 people and wounding around 500.