Dan Stevens, the county's emergency management spokesman, said five or six people were reported stabbed at about 7:20 a.M. (local time) at Franklin Regional High School, about 25 kilometres east of Pittsburgh.
It was not immediately clear if the suspect and the victims are students, adults or a mix of both. It does not appear that any of the victims suffered life-threatening injuries, Stevens said, though several helicopters were seen flying people from the scene to area hospitals.
The high school was on lockdown, and students were being kept there as a precaution as school and law enforcement officials double-checked the premises.