A shooter is dead after opening fire at North Park Elementary School in San Bernardino, Calif., KNBC-TV reported.

Officials said there were four victims in a murder-suicide incident, KTLA reported.

Two adults — a female teacher and a male shooter — were killed. The male shooter died of a self-inflicted gunshot wound.

Two wounded students were flown to a hospital where an 8-year-old later died. The other student was listed in critical condition.

RELATED: “At least” four shot, two killed at California elementary school in possible murder-suicide

Authorities said the shooter had an existing relationship with a North Park teacher who was a victim, but they have not provided details about the adults’ relationship.

“We believe the teacher knew who the shooter was,” San Bernardino City Unified School District spokeswoman Maria Garcia told  KNBC.

The shooter was identified, but his name has not been released, San Bernardino police Capt. Ron Maass said.

According to KTLA, the classroom may have been a mix of third and fourth grade students.

The children who were shot were not related to the adults and are not believed to have been intentionally targeted, authorities said.

One child has been reunited with family, KTLA reported.

Other children at North Park were taken to nearby Cajon High School, where parents were told that they could pick them up after showing identification.

Officials said parents could expect hours-long delays in reuniting with their children as identifications are verified and students are interviewed as witnesses.

“Our hearts are broken,” said Dale Marsden, the superintendent of the San Bernardino City Unified School District.

North Park’s campus is safe, authorities said, but Marsden said the school will be closed for at least two days while authorities investigate.

North Park Elementary has about 600 students in kindergarten through sixth grades, according to The Associated Press. The school does not have security officers on campus on a daily basis.

According to Maass, the shooter signed in at North Park’s front desk before going to the classroom, where he opened fire.

“There was no indication the gun was visible upon his arrival at the school,” Maass said.

The shooter said he was going to the classroom to visit the teacher.

Marsden said general policy for adult visitors to classrooms involves showing identification and stating purpose of the visit.

San Bernardino Mayor R. Carey Davis said President Donald Trump called to express concern and support.

In December 2015, husband and wife Syed Rizwan Farook and Tashfeen Malik shot and killed 14 people and wounded 22 others after ambushing a training event at the Inland Regional Center in San Bernardino.