None of the injuries appear to be life threatening.
Durham Regional Police Sgt. Bill Calder said officers were called to Dunbarton High School in Pickering, Ontario today morning.
He says four people were stabbed by the student, whose name and age have not been released.
Calder said charges are pending, but would not comment specifically on which ones she might face.
The school remains in lockdown as police continue to investigate, Calder said, adding that more details are expected later in the day.