A man plowed a white rental van into a crowd of pedestrians in the center of Canada's biggest city Toronto on Monday, police said, with several people feared dead.
Police said up to 10 people were struck, adding they could not confirm any deaths, but local media reported at least four fatalities in the incident.
Television images showed the man and a police officer facing off, their guns drawn. The suspect eventually surrendered his weapon and was taken into custody.
Vehicle attacks have been carried out to deadly effect by extremists in a number of capitals and major cities, including London, Paris, New York and Nice, but the motive for Monday's incident was not yet clear.
"Update: unknown of extent of injuries, possible 8 - 10 pedestrians struck," Toronto police wrote on Twitter.
Police then said it was "too early to confirm the number of pedestrians struck or their injuries."
At least one body was seen covered at the scene. At least seven patients were being treated at the Sunnybrook Health Sciences Centre, the facility said on Twitter.
- 'Really fast' -
Officers were called to the scene -- on Yonge Street at the corner with Finch Avenue -- at 1:27 pm (1727 GMT), police said.
A white rental van with a dented front bumper was stopped on the sidewalk of a major intersection, surrounded by police vehicles.
"He was going really fast," witness Alex Shaker told CTV television.
"All I could see was just people one by one getting knocked out, knocked out, one by one," Shaker said. "There are so many people lying down on the streets."
Another witness, Jamie Eopni, told local Toronto television station CP24: "It was crashing into everything. It destroyed a bench. If anybody was on that street, they would have been hit on the sidewalk."
Canadian Prime Minister Justin Trudeau told the House of Commons: "Our hearts go to anyone affected."
"We are going to have more to learn and more to say in the coming hours," he added.
- 'It's frightening' -
The incident occurred as Toronto was hosting foreign and public security ministers from the G7 leading industrialized nations -- Britain, Canada, France, Germany, Italy, Japan and the United States.
Authorities have not yet stated what the driver's motives may have been.
"We have no information on that point and we need to wait until there's information before we comment... I will respect the expertise of the security officials," Ontario Premier Kathleen Wynne told reporters when asked if the incident was terror-related.
"We are all unsettled and very disturbed by a situation like this, it's impossible not to be -- it's frightening."
Canada has only rarely been the scene of terror attacks.
In October, a man stabbed a police officer in the western city of Edmonton before slamming his van into a group of pedestrians, injuring four people.
And in Quebec in October 2014, a Canadian man ran over two soldiers in a parking lot with his car, killing one of them. The driver was shot dead by police when he attacked them with a knife.
In March 2016, a Canadian who claimed to have radical Islamist sympathies attacked two soldiers at a military recruitment center in Toronto.