The gunman was fatally shot by sheriff's deputies. His name has not been released. The Tehama County Sheriff's Department said they were dealing with at least five separate crime scenes and were trying to assess the number of casualties.
Authorities said the shooting occurred around 8 a.m. in Rancho Tehama, near Red Bluff, about 120 miles northwest of Sacramento.
Tehama County Assistant Sheriff Phil Johnston did not have a total number of victims, but said that "a number" of students had been medically evacuated from the school grounds. A rifle and handguns were recovered at one scene, he said.
"We have about 100 law enforcement personnel in Rancho Tehama right now, with multiple, multiple scenes," Johnston said.
"I know that we have [airlifted] a number of students," he told reporters. "I know that we have children that were attending school in a safe location at this time."
Officials said the Rancho Tehama area remains on lockdown.
Nearby residents and business owners said they heard at least 100 gunshots.
"I thought this only happens to places like L.A. or New York," said Jose Garcia, owner of La Fortune Convenience, told the Los Angeles Times.
Coy Ferreira, a parent at the school, told KRCR-TV that he heard a series of gunshots through a classroom window and saw one young boy shot in the foot and chest and a second student shot in the arm. Both were alert and conscious, he said.
The owner of a nearby cafe, Coffee Addiction, told The Times that she called 911 after hearing gunfire and screaming at the elementary school.
The woman, who identified herself only as Tiffany, said she heard about 100 rounds fired from what sounded like multiple guns.
The business owner said she and her husband and their four children moved to the area from Redding about seven years ago. She said that they have always felt safe.
"It's a great community," she said. "I am hoping it doesn't get some kind of bad rap because of one person in one area."
Rancho Tehama has a population of about 1,485, according to a census estimate.
The school and surrounding community were on lockdown.
"We have had an active shooter incident at Rancho Tehama Elementary this morning," read a statement from the Corning Union Elementary School District website. "There are confirmed injuries. We are cooperating with law enforcement during this investigation but do not have specific details at this time."
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