Police have closed down St. Georges Avenue between North Street and Chestnut this morning.
There are multiple police vehicles on scene, including the city's armoured unit.
At least one man appears to have been taken into custody.
Paramedics and firefighters appear to be standing by at the former St. Basil Secondary School site.
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(EDITOR'S NOTE: An earlier version of this story incorrectly indicated that the police presence was in the hilltop area)