At least 10 people were killed and 15 others injured as a rented van plowed down a crowded Toronto sidewalk on Monday, Canadian authorities said.
Toronto Police Chief Mark Saunders identified the man detained after the incident as Alek Minassian, 25, a resident of the Toronto suburb of Richmond Hill.
The Police Chief said the suspect had not been known to police previously, reports AP.
Witnesses said the driver was moving fast and appeared to be acting deliberately, but police officials would not comment on the cause or any possible motive.
Speaking at a news conference Monday night, Mr. Saunders raised the initial death toll of nine to 10, saying another victim had died at a hospital. He said 15 others were hospitalised.
Asked if there was any evidence of a connection to international terrorism, the chief said only, "Based on what we have there's nothing that has it to compromise the national security at this time."
But a senior national government official said earlier that authorities had not turned over the investigation to the Royal Canadian Mounted Police, a sign that investigators believed it unlikely terrorism was the motive. The official agreed to reveal that information only if not quoted by name.
Authorities released few details in the case, saying the investigation was still underway, with witnesses being interviewed and surveillance video being examined.
"I can assure the public all our available resources have been brought in to investigate this tragic situation," Toronto Police Services Deputy Chief Peter Yuen said earlier.
The incident occurred as Cabinet ministers from the major industrial countries were gathered in Canada to discuss a range of international issues in the run-up to the G7 meeting near Quebec City in June. Canadian Public Safety Minister Ralph Goodale called the incident a "horrific attack" and said the G7 foreign ministers extended their condolences.
The driver was heading south on busy Yonge Street around 1:30 pm and the streets were crowded with people enjoying an unseasonably warm day when the van jumped onto the sidewalk.
Ali Shaker, who was driving near the van at the time, told Canadian broadcast outlet CP24 that the driver appeared to be moving deliberately through the crowd at more than 30 mph.
"He just went on the sidewalk," a distraught Shaker said. "He just started hitting everybody, man. He hit every single person on the sidewalk. Anybody in his way he would hit."
Witness Peter Kang told CTV News that the driver did not seem to make any effort to stop.
"If it was an accident he would have stopped," Kang said. "But the person just went through the sidewalk. He could have stopped."
Video broadcast on several Canadian outlets showed police arresting the driver, dressed in dark clothes, after officers surrounded him and his rental Ryder van several blocks from where the incident occurred in the North York neighborhood of northern Toronto. He appeared to make some sort of gesture at the police with an object in his hand just before they ordered him to lie down on the ground and took him away.
Witness Phil Zullo told Canadian Press that he saw police arresting the suspect and people "strewn all over the road" where the incident occurred.
"I must have seen about five, six people being resuscitated by bystanders and by ambulance drivers," Zullo said. "It was awful. Brutal."
Police shut down the Yonge and Finch intersection following the incident and Toronto's transit agency said it had suspended service on the subway line running through the area.
Prime Minister Justin Trudeau expressed his sympathies for those involved. "Our hearts go out to everyone affected," Trudeau said in Ottawa. "We are going to have more to learn and more to say in the coming hours."