A teacher has been killed and two children injured in a shooting at a San Bernardino elementary school.
The male shooter entered North Park Elementary School, signing in at the front desk to visit the female teacher with a concealed handgun.
He was allowed entry to the school and went to her mixed-grade classroom where he opened fire on her and two children standing near her before turning the gun on himself, Daily Mail reports.
Police found him and the teacher shot dead in the classroom. The two children, whose ages are not known, were taken to hospital in critical condition. North Park Elementary School teaches from kindergarten to Grade 6 between the ages of five and 12.
Parents told KTLA they believed they were in third or fourth grade, putting them between the ages of eight and 10.
The incident is believed to be a domestic-related murder suicide aimed at the teacher. The children are not related to either the teacher or the shooter.
It is not yet known whether anyone else was inside the classroom at the time or if the gunman intended to shoot the children.
Police are still trying to inform one child's family of their involvement in the tragedy.
San Bernardino Police confirmed at a press conference that the shooter signed in at the front desk and was known to other staff who did not know he was carrying a gun when he was allowed entry.
From the front desk, he walked to the female teacher's classroom where he opened fire.
"The entire incident is limited to a single classroom. The suspect had come to visit the female victim," Captain Ron Maas of the San Bernardino Police Department said.
Authorities are working to confirm the identifies of both the shooter and teacher but they say the pair are known to each other. Police were searching the man's house on Monday afternoon.
"The children, we do not believe were targeted. (They were) the unfortunate recipients of injuries by being in proximity to the female at the time."
Police do not yet know how many shots were fired in total. All of the 520 other children in the school were immediately evacuated afterwards.
They were seen making their way across the playground holding hands before being put on buses to leave the scene.
They were taken to California State University San Bernardino to be counted by school officials and interviewed by police if necessary.
Parents are being told to go to Cajon High School to have their IDs checked. They will then be able to reunite with their children either at the university or at Cajon High school.
Some parents, who rushed to the scene of the shooting immediately after news of it broke on Monday morning, were able to go home with their families straight away.
One young student described being evacuated from her P.E. class after being reunited with her mother outside the school. Others had to settle for catching a glimpse of their children as they were put onto a bus.
"All of the kids started running out. It was pretty scary," the child said through tears.
SWAT tanks and anti-terrorism were among forces deployed to the school as the situation unfolded.
San Bernardino Mayor Carey Davis said President Trump had offered his condolences and assistance in a phone call on Monday morning.
"This is a tragic event. It's going to take time for ourr heads, our hearts to heal," Mayor Davis said.
The San Bernardino Fire Department first reported 'multiple' gun shot wound victims at the school.
North Park Elementary School is just nine miles from the Inland Regional Center where 14 were killed and 22 were injured in the 2015 San Bernardino terrorist attack.