At least one student was shot and injured at an elementary school after shootings occurred at seven separate scenes near the town of Red Bluff.
A second child and a female adult were shot in a truck, authorities said.
According to police, it appears that the shooter was randomly picking targets.
Police said they were aware of a "domestic violence incident" that had taken place at some point involving the alleged shooter.
VIDEO: Officials give update on deadly NorCal shootings
VIDEO: Officials give update on deadly NorCal shootings
The gunman was killed after two officers engaged him, law enforcement officials said. The gunman had a semi-automatic rifle and two handguns.
At least ten people were hospitalized after the shooting spree.
Mercy Dignity Health confirmed that the hospital has received three patients. Enloe Hospital received four, according to hospital officials.
Police confirmed that students were among those transported to hospitals.
Details were still sketchy hours after the shooting and authorities didn't have a firm count of the wounded due to the number of places where the gunman opened fire in the community of Rancho Tehama Reserve, about 130 miles north of Sacramento, Tehama County Assistant Sheriff Phil Johnston said.
"It was very clear at the onset that we had an individual that was randomly picking targets," Johnston said.
He declined to release the name of the shooter but said the gunfire began with a domestic violence incident that neighbors reported.
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.
About 100 students attend the school, which is the scene of one of the shootings that took place, according to an official.
A man in the area said his roommate was among the victims in Northern California and that his neighbor was the gunman.
Brian Flint said that his neighbor, whom he knows only as Kevin, also stole his truck.
Authorities recovered a semi-automatic rifle and two handguns reportedly used by the shooter.
VIDEO: Officials report several dead after shooting in Tehama County
Officials say 3 dead after shooting in Tehama County
Flint said he and his roommate told authorities that their neighbor was acting "crazy" and threatening them.
Flint said the neighbor had been shooting "hundreds of rounds" from large magazines. The incident was over after about 45 minutes.
California Gov. Jerry Brown issued a statement in the wake of the shooting:
"Anne and I are saddened to hear about today's violence in Tehama County, which shockingly involved schoolchildren. We offer our condolences to the families who lost loved ones and unite with all Californians in grief."
The Associated Press contributed to this story.