Toronto was under heavier-than-usual police protection on Thursday due to an unspecific "potential risk to safety" in Canada's largest city, police said without providing details.

Heightened security, including emergency response teams, was visible around tourist sites such as the CN Tower and a nearby aquarium in downtown Toronto. The city's police said the increased presence was due to an "unconfirmed, uncorroborated piece of information" related to the Greater Toronto Area.

In April, a Canadian man plowed a van into pedestrians on a crowded Toronto sidewalk, killing 10 people in Canada's deadliest mass killing in decades.