A van traveling at a high rate of speed left the road Monday and mounted a sidewalk in Toronto, killing 10 and injuring 15.
The incident occurred around 1:30 p.m. EST (1730 GMT) in a busy section in the north end of the city.
Alek Minassian was arrested near the scene of the mayhem beside a white passenger van that is suspected to be the vehicle used in the incident.
Minassian, 25, lists himself on his LinkedIn page as a student at Seneca College in Toronto.
The attack is not part of a wider plot and there is no threat to national security, said Canadian Public Safety Minister Ralph Goodale.
"I've had the opportunity to consult with senior officials of the security and police agencies of the Government of Canada, and on the basis of all available information at the present time, there would appear to be no national security connection to this particular incident," he told reporters at a press conference.
But he did not discount the possibility that it could be an individual terrorist act.
While police are being tight-lipped about information on the incident, witnesses said they saw tarps over four people lying on the sidewalk.
The trauma unit at the nearby Sunnybrook Hospital issued a statement saying it had received seven victims after "an incident involving a van striking a number of pedestrians".
A hospital spokesperson later said one patient had died and several were in critical condition.
An eyewitness said there were "a lot of people lying lifeless on the ground".
Bystanders tried to revive them, but to no avail.
Subway service has been suspended in the area.
Prime Minister Justin Trudeau was apprised of the situation and commented on the incident from Ottawa.
"Our hearts go out to anyone affected," he said. "We're obviously going to have more to learn and more to say in the coming hours."
All available personnel have been called in to investigate the incident, police said.
"I want to assure the public that the rest of the city [is] adequately policed," Toronto Deputy Police Chief Peter Yuen told reporters at a press conference.
The identities of the victims have not yet been released.
No motive for the incident has been determined as yet, police said.
