Local authorities have revealed the shooting broke out in a home in Tehama County and continued at the Rancho Tehama Elementary School.
Assistant Sheriff Phil Johnston told San Francisco news network KCRA that the shooter was killed by police.
Sheriff Johnston also said he was unaware of the number of victims, but could confirm the number was at least five.
'I know that we have [flown] 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.
'It was very clear early on that we had a subject that was randomly picking targets,' he continued.
While details about what led up to the shooting were unclear, Mr Johnston said authorities were told by neighbours that 'there was a domestic violence incident' involving the suspected attacker.
He added that some 100 law enforcement officers had responded to the shooting.
There were at least five crime scenes, he said.
A hospital spokeswoman said seven people, including children, were being treated for injuries. She refused to say what condition the victims were in.