Nine people are dead and 16 injured after a van jumped a kerb on a busy intersection in Toronto, Canada, striking people before racing from the scene.
The driver was later found and taken into custody.
A witness, Phil Zullo, told Canadian Press that he saw police arresting a man who had been driving a Ryder rental truck on Monday afternoon (Tuesday morning NZT) and saw people "strewn all over the road" where the incident occurred.
"It must have seen about five, six people being resuscitated by bystanders and by ambulance drivers," Zullo said. "It was awful. Brutal."
"He started going down on the sidewalk and crumbling down people one by one," Alex Shaker, who was driving down Yonge Street, told CTV News. "He just destroyed so many people's lives."
Toronto's acting police chief Peter Yuen confirmed the deaths shortly after 8.45am (NZT)
Seven patients had been taken to the city's Sunnybrook Hospital, with the emergency department going into a precautionary lockdown, CBS reported.
"At this point it's too early to tell what if any motive there was," Toronto police spokeswoman Meaghan Gray said.
Toronto paramedic spokeswoman Kim McKinnon said first responders were on scene treating multiple patients, but wouldn't confirm the number or severity of injuries.
Police shut down the Yonge and Finch street intersection following the incident and Toronto's transit agency said it has suspended service on the subway line running through the area.
The incident occurred at around 1.30pm local time (5.30am Tuesday NZT) 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.
"Obviously we're just learning of the situation in Toronto. Our hearts go out to anyone affected. We're obviously going to have more to learn and more to say in the coming hours," Canadian Prime Minister Justin Trudeau said