Police said they lifted a partial lockdown at the University of Toronto Monday afternoon, hours after getting reports of a man dressed in all black with a backpack and mask -- and possibly a gun.
Officers had taken a man into custody but released him without charges, police told CBC News.
Toronto Police Chief Mark Saunders said he saw a photo of the possible gunman wearing a surgical kind of mask.
Police were working to clear some of the buildings at the University of Toronto. It is in the neighborhood around Ontario's provincial legislature. Several units, including the Emergency Task Force, were on the scene.
"It's clear to say that we live in a different time right now," Saunders said when asked if the public should be proactive in reporting suspicious activity following the nightclub shooting in Orlando, Florida, that was that was the worst mass shooting in U.S. history.
Toronto Const. Allyson Douglas-Cook said the reports came from a building that is under construction on the University of Toronto campus. She said building security didn't recognize someone wearing a mask, but police are uncertain if the person is a construction worker.
The University of Toronto, which surrounds the legislature, said a number of buildings on its downtown campus have been closed while police investigate.
All southbound lanes of a major street near the provincial legislature have also been closed.