A special education teacher and one of her students have been fatally shot by her estranged husband when he opened fire in her classroom before killing himself at a primary school in California.

A second student was wounded by the gunman, who authorities said had a criminal history that included domestic violence and weapons charges.

US police say the man, identified as Cedric Anderson, had a criminal history that included domestic violence and weapons charges.

The two students, both boys, were believed to have been caught in the gunfire unintentionally as bystanders to Monday's shooting in San Bernardino, which took place about 13km from where a radicalised Muslim couple killed 14 people in a December 2015 shooting rampage.

City Police Chief Jarrod Burguan said the shooting at North Park Elementary School was an apparent murder-suicide. It was the latest in dozens of cases of gun violence on school campuses around the US each year.

The gunman's wife was identified as Karen Elaine Smith. Burguan said the couple had been married briefly and had been separate for about a month or month and a half.

The two students struck by gunfire had been standing behind Smith, the chief said.

One eight-year-old boy died from his wounds. A nine-year-old classmate was admitted to paediatric surgery at a local hospital, where he was said to be in stable condition.

Neither student was related to the dead couple.