The shooting broke out at a home in Tehama County and continued at the Rancho Tehama Elementary School, local authorities were quoted as saying.
Assistant Sheriff Phil Johnston told San Francisco news network KCRA that the assailant was killed by police.
He said he didn’t have the exact number of victims but knew of at least three deaths.
“I know that we have medevacked (airlifted) a number of students, I know that the school has been cleared, I know that we have the children that were attending school in a safe location at this time,” he said.
He added that some 100 law enforcement officers had responded to the shooting.