Ursuline Catholic College was placed in a brief hold and secure Tuesday afternoon after an incident during the senior lunch break.
Chatham-Kent police were called to the school around 12 p.m. after a number of young adults arrived at the school and refused to cooperate with a request from school staff to leave the area.
"Due to the unknown reason for their presence on the property and their unwillingness to cooperate with a request from our staff to leave the immediate area, a decision was made to contact Chatham-Kent Police Services," said Ursuline Catholic College Principal Ray Power.
While police were on site investigating, the school was placed on hold and secure. It was lifted at 1:40 p.m.
"A Hold & Secure is placed in effect as the result of an external situation, which may or may not be related to the school," said Power. "During this protocol, external doors are locked and monitored by staff."
Officials said because the hold and secure was placed during lunch, grab bags from the breakfast program were made available to students.
Chatham-Kent police are continuing to investigate.