The US state of California is reeling from its second mass shooting in days after a man shot dead seven former co-workers south of San Francisco.

It comes as the state mourns the death of 11 at Monterey Park - about six hours south east of Half Moon Bay - during Lunar New Year celebrations.

A number of children who had recently been let out of school and lived on the rural property saw the attack take place, San Mateo County Sheriff Christina Corpus said.

San Mateo County Board of Supervisors President Dave Pine told the Associated Press news agency that the attacks were committed by a "disgruntled worker".

Just hours after the attack, seven were injured and one person was killed in a shooting in Oakland - about 40 miles (64 km) northeast of Half Moon Bay.

Even as details of the deadly attack in Half Moon Bay were coming in, detectives in the south of the state were still hunting for a motive for the killings in Monterey Park.