Among the dead are the gunman, who was killed by police, authorities said.
"Rancho Tehama resident Salvador Tello said he was taking his three children to school when the gunman fired at a truck in front of him".
An exact number of injured victims isn't known at this time, but police in California have confirmed that a number of students have been transported to hospital.
Jeanine Quist, an administrative assistant with the Corning Union Elementary School District, said no one was killed at the school but a "number" of students were shot and wounded. Students also were shot and wounded at an elementary school. Officials said they are actively searching for the shooter.
Another witness, Casey Burnett, said the gunman was "driving around and shooting randomly from his vehicle".
Authorities have recovered a semiautomatic rifle and two handguns after the shootings in the rural subdivision described on its website as a "quiet private country community" where "the people are friendly and the pace is relaxed".
Enloe Medical Center in Chico tells NPR that it has received five patients, three of whom have been treated and released.
The shooter was killed by law enforcement. There are just four teachers on staff; each teaches at least two grades, according to the school newsletter.
Posts on social media showed Rancho Tehama Road being closed off with yellow crime tape, and students' parents stuck behind the road block.
Gov. Jerry brown issued a statement on the shooting, saying: "Anne and I are saddened to hear about today's violence in Tehama County, which shockingly involved schoolchildren".