A gunman who critically wounded two kindergarteners at a tiny religious school in Northern California believed by targeting children he was carrying out “counter-measures” in response to America’s involvement in Middle East violence, a sheriff says.

Glenn Litton used a “ruse” of pretending to enrol a fictitious grandson to gain entry to the Feather River School of Seventh-Day Adventists in Oroville, Butte County Sheriff Kory L Honea said.

Litton, who had a mental illness, used a so-called ghost gun, which is difficult for investigators to trace, to shoot two kindergarten boys, ages 5 and 6, who remained in critical condition, the sheriff said. Litton died at the scene, authorities said. 

While Honea said Litton, 56, also had a lengthy criminal history — mostly theft and identity theft — authorities said they did not find any violent crimes on his record.

Honea said the man is believed to have targeted Feather River School of Seventh-Day Adventists in Oroville in the attack, though it was unclear why.

Litton had attended a school of Seventh-Day Adventists in another town as a child, the sheriff said, and he possibly had a relative who attended Feather River as a young child.

But in Litton's writings, the sheriff said, the suspect wrote about taking “counter-measures” against the school in response to America’s involvement in violence in the Middle East.

“That’s a motivation that was in his mind,” Honea said.

"How it was that he conflated what’s going on in Palestine and Yemen with the Seventh-Day Adventist Church, I can’t speculate. I’m not sure that we’ll ever know that."

He said Litton had similarly scheduled an appointment at another Seventh-Day Adventist school.

The shooting occurred shortly after 1pm at the private K-8 Christian school with fewer than three dozen students in Oroville, on the edge of the tiny community of Palermo, about 104km (65 miles) north of Sacramento.

Eyewitness footage captures emergency services arriving at school. – Reuters

Law enforcement officials have documented Litton's history of mental illness back to when he was a teenager.

In recent years, Litton searched online for guns and explosives and wrote notes to himself to plan a non-specific mass incident, though Butte County District Attorney Michael L Ramsey said they were “just ruminations".

Litton was a convicted felon and therefore could not legally possess a firearm.

The sheriff said the 6-year-old suffered two gunshot wounds that caused internal injuries, while the 5-year-old was shot once.

“The fact that they are currently still with us is a miracle,” Honea said of the children

He added they would likely face additional surgeries and “have a very long road ahead of them, in terms of recovery”.

Honea said the gunman was dropped off by an Uber driver for a meeting with a school administrator.

Sheriff's deputies walks past a playground outside Feather River Adventist School after the shooting. – AP

The small rural school was closed a day after the shooting but sheriff’s deputies walked around the campus behind shuttered gates in the morning and staff members carried classroom items out to their cars.

Shawn Webber, an Oroville city council member, said the region was reeling.

“When you see this on the news or nationally and it’s like, those things don’t happen here. Well, yesterday it happened here,” he said.

“It just absolutely violated the peace of our community.”

A candlelight vigil is planned for Friday.

It was the the latest among dozens of school shootings across the US in recent years, including especially deadly ones in Newtown, Connecticut, Parkland, Florida, and Uvalde, Texas.

The shootings have set off fervent debates about gun control and frayed the nerves of parents whose children are growing up accustomed to active shooter drills in their classrooms.

But school shootings have done little to move the needle on national gun laws.

Firearms were the leading cause of death among children in 2020 and 2021, according to KFF, a nonprofit that researches healthcare issues.

Two children critical after Northern California school shooting. – AP

Laurie Trujillo, a spokesperson for the Northern California Conference of the Seventh-Day Adventist Church, said they were "deeply saddened by the events that occurred today at our Feather River school".

“We know that the close-knit Feather River community will be grieving for a long time, as will the rest of our conference,” said Trujillo. 

She added that they were grateful to the sheriff's office for acting quickly to protect the students.

Sixth grader Jocelyn Orlando described what happened.

"We were going in for lunch recess and basically everybody in my classroom heard shooting and most people were screaming," she said.

"We all went into the office, we closed the curtains, locked the doors, basically did what we would do in a school shooting, and then one of the teachers came and we all ran into the gym."