CALGARY -- A Calgary high school was placed under lockdown for just over an hour Tuesday after a woman acting erratically entered the building.

A note to parents says the woman went into Bishop O'Byrne High School just after 1 p.m., as the lunch period was ending.

Police were called and the lockdown procedure was initiated.

"CPS responded quickly and escorted the woman from the school," read a note from principal Monique Baker to parents. "Police checked the entire building, including the Cardel complex and determined the school was safe."

The lockdown was lifted about 2:30 p.m.

Police said the woman was suffering from a mental health issue and was removed from the building but not arrested.