Several people were transported to the nearby Henry Mayo Newhall Hospital. The suspect of the shooting was taken into custody at hospital, Los Angeles County Sheriff Alex Villanueva tweeted.
Police responded to reports of shots fired at about 7:40 a.m. local time at the school, around 40 miles north of Los Angeles.
The locals have been told to avoid the area and not to block roadways as emergency vehicles are still responding.
A nearby church has been used as a reunification center for parents and students from the school.