A suspect was in custody after seven people were killed in two related shootings at a mushroom farm and a trucking firm in a coastal community south of San Francisco, officials said.
San Mateo County Board of Supervisors president Dave Pine says four people were killed at the farm and three at the trucking business on the outskirts of Half Moon Bay, a city about 30 miles south of San Francisco.
The police have arrested 67-year-old Zhao Chunli in connection with the shooting, Pine said.
He described the suspect as a “disgruntled worker”.
The San Mateo County Sheriff’s Office tweeted just before 5pm (1am UK) that a suspect was in custody.
“There is no ongoing threat to the community at this time,” the sheriff’s office said.
Television footage from the area showed officers taking a man into custody without incident.
Aerial television images also showed police officers collecting evidence from a farm with dozens of greenhouses.
The shooting followed the killing of 11 people late on Saturday at a ballroom dance hall in Southern California.
“We are sickened by today’s tragedy in Half Moon Bay,” Mr Pine said in a statement.
“We have not even had time to grieve for those lost in the terrible shooting in Monterey Park. Gun violence must stop.”
California Governor Gavin Newsom tweeted that he was “at the hospital meeting with victims of a mass shooting when I get pulled away to be briefed about another shooting. This time in Half Moon Bay. Tragedy upon tragedy”.