Gunfire erupted in an elementary school classroom in the California city of San Bernardino on Monday in what police said they believe is a case of "murder-suicide" resulting in multiple injuries.

"Preliminary info is 4 victims, being treated," city police chief Jarrod Burguan wrote on Twitter. "Suspect is possibly down as well," he added, though it was unclear if that meant the shooter was killed or apprehended.

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

Students at North Park Elementary School were being transported to a nearby high school "for safety," Burguan said.

San Bernardino is located about an hour's drive east of Los Angeles.

In December 2015, a newlywed couple apparently inspired by the Islamic State group opened fire on an office party in San Bernardino, killing 14 people and injuring 22 others.

AFP