Monday morning lockdown at Innisfil high school

Students in a classroom in this undated file image. CTV NEWS

Simcoe high school students and staff started the school week under lockdown.

Police say officers were called to Nantyr Shores Secondary School on Anna Maria Avenue in Innisfil just before 8 a.m. after a reported threat.

The public school was placed in a hold and secure for investigation, but authorities later determined there was no concern for student or staff safety.

The hold and secure was lifted at approximately 9:30 a.m.

Throughout the investigation period, all exterior doors were locked preventing any one to enter or exit the building, but normal operations continued inside.

The Simcoe Country District School Board has sent out a formal letter to all families of students.