Tehama County Assistant Sheriff Phil Johnston said that officers are investigating at least five crime scenes in and around the school in Rancho Tehama Reserve, about 130 miles north of Sacramento.
The suspected shooter was shot and killed by law enforcement, officials confirmed.
Some students at the school were medically evacuated; it's not clear yet how many people were injured in the shooting.More news: Russia Used Video Game Screenshots to "Prove" the US Is Assisting ISIS
"We made it aware that this guy is insane and he's been threatening us", he said. One student was shot at an elementary school and second child was shot in a truck. At least three children and one adult were transported to Enloe Medical Center, in Chico, California, the hospital confirmed to KHSL.
Mr Johnston said police were alerted to the shooting at around 8am local time (4pm GMT). "That evolved into multiple victims and multiple shots at the school", the deputy said.
The shooter reportedly wounded kids at the school.More news: Chevrolet Unveils Their Fastest Corvette Ever
The school district was cooperating with local law enforcement, according to its statement. The FBI also "is sending some teams up to assist at the request of Tehama County authorities", said Jason Wandel, chief division counsel at the FBI's Sacramento field office.
A neighbor of the shooter spoke with the media and said that the suspect was acting "crazy", and that the suspect threatened him and his roommate before stealing his truck. He declined to release the name of the shooter but said the gunfire began with a domestic violence incident that neighbors reported.
Fox 5 in San Diego reports the shooting started at a home and moved to the elementary school.More news: Anti-Trump protesters, police engage in brief scuffle in Manila
"Grateful to the officers and first responders on the scene", she tweeted.