Special ed teacher and 8-year-old student killed in US primary school shooting.

A teacher and an eight-year-old male student have been shot dead and a second student critically wounded in a murder-suicide at a San Bernardino primary school.

A man named as Cedric Anderson, 53, opened fire with a pistol in a special education classroom at the Southern California primary school, fatally shooting the teacher, Karen Elaine Smith, and wounding the two students before killing himself.

Police said the boy, identified as Jonathan Martinez, had died of his injures in hospital, the LA Times reports. Another nine-year-old boy is in a stable condition.

The gunman was the husband of the teacher shot dead, police say, adding that the wounded children were standing behind her.

It is understood the couple had only been married a few months and were “estranged”.

Police said the two children were believed to have been caught in the gunfire unintentionally as bystanders to Monday’s violence, which unfolded several kilometres from the scene of a December 2015 shooting rampage that killed 14 people.

San Bernardino Police Chief Jarrod Burguan said the shooting at North Park Elementary School in San Bernardino, east of Los Angeles, was an apparent murder-suicide.

"The children we do not believe were targeted," police Captain Ron Maass told reporters.

The 600 other students at the school were bused to safety at California State University's San Bernardino campus, several kilometres away.

Police said she and the gunman were the only adults in the classroom.

We believe this to be a murder suicide. Happened in a class room. Two students have been transported to the hospital.

— Chief Jarrod Burguan (@SBPDChief) April 10, 2017

Two adults are deceased in a classroom, believed to be a murder suicide. We believe the suspect is down and there's no further threat.

— Chief Jarrod Burguan (@SBPDChief) April 10, 2017

The gunman had gained entry to the school as a visitor and kept his weapon concealed until he opened fire inside the classroom.

Aerial television footage from the scene showed children holding hands and walking single-file across the campus from the school building to waiting buses.

One young student, reunited with her mother, told local NBC News affiliate KNBC-TV that the incident left her "super scared".

As word of the shooting spread, panicked parents raced to the school, some in tears, some praying as they anxiously sought information about their children. They were told to go to a nearby high school where they would be reunited.

Anxious parents interviewed on camera said they had been given no information from the school other than where their children were being taken.

The city of San Bernardino last made national headlines on Decembre 2, 2015, when a husband and wife who authorities said were inspired by Islamic extremism opened fire on a holiday office party of county health workers, killing 14 people and wounding more than 20.

The couple, Syed Rizwan Farook and Tashfeen Malik were killed by police during a shootout.

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