When officers arrived, the woman was using the cleaver to hit and cut herself in her upper body, Findlen said.
Two of six officers on the scene opened fire after the woman charged them with the cleaver, Findlen said. He was not sure how many times she was hit.
The woman was pronounced dead at local hospital. Police have not released her name, but said she was in her 50s. Police did not know what connection, if any, she may have had with the school.
During the incident, the school was locked down. School officials were releasing students to their parents around 4 p.m.
No students or school personnel were hurt. Findlen credited school officials with "quickly locking down and getting students into locked classrooms."
The officers who opened fire have been placed on routine paid administrative leave while Modesto police and the Stanislaus County District Attorney's Office investigate.