Two people were killed Monday at an elementary school classroom in the California city of San Bernardino in what police said was a case of "murder-suicide."

"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," city police chief Jarrod Burguan wrote on Twitter, adding that two other people, possibly students, were wounded and taken to hospital.

It was not immediately clear if that meant the shooter was among the dead.