Police and ambulance were called to Whanganui High School on Tuesday afternoon for a "serious incident" between two staff members.
Board of Trustees chairman Randal Southee said lessons had finished for the day when the incident occurred in one of the offices of the main administration building.
"This incident requiredpolice intervention and is currently subject to a police investigation as well as a Board of Trustrees' investigation," he said.
St John Whanganui territory manager John Stretton said paramedics were called at 3.17pm to assess a 60-year-old woman, but the patient had left by the time they arrived at 3.23pm.
Mr Southee said support was being provided for the staff involved.
