Nine people have killed and 16 injured after a man drove a van into pedestrians in Toronto, police said.
The driver fled the scene of the incident, at a busy intersection in the north of the Canadian city.
He was arrested several blocks away and taken into custody. Authorities said they had not yet established a motive for the apparent attack.
Reza Hashemi, who owns a video shop on Yonge Street, told the BBC he heard screaming on the other side of the road.
Mr Hashemi said the driver mounted the pavement, ran into people, and returned to mount the pavement again.
The incident occurred at Yonge Street and Finch Avenue at 13:30 local time (17:30 GMT) on Monday. The crime scene encompassed a 2km (1.24 mile) stretch of Yonge Street.
About 18 miles (30km) away, downtown, the Group of Seven foreign ministers of industrialised nations – including Canada, the US, Britain, France, Germany, Italy and Japan – were holding meetings.
Pictures apparently taken at the scene showed police armed with rifles and paramedics treating injured people. One orange bag, which appeared to contain a body, was loaded on to an ambulance.
“Reports were that a white van mounted the kerb, drove down the sidewalk at southbound Yonge, south of Finch, and struck eight to 10 people possibly, the numbers aren’t confirmed yet,” Toronto police spokesperson Gary Long told Canadian broadcaster Global News.
Toronto police spokeswoman Jenifferjit Sidhu told CBC News that the vehicle was stopped by police. No description was given of the driver, including name, age or gender.
Canadian Prime Minister Justin Trudeau tweeted from Ottawa: “Our thoughts are with all those affected by the terrible incident at Yonge and Finch in Toronto.”
“Thank you to the first responders working at the scene – we’re monitoring the situation closely.”
Speaking in broken English, one witness told local media: “I saw there’s a white truck just go to the sidewalk and so many people just are shouting, ‘stop the car!’ But he just keep moving and he hit some people and three people lie down there and they didn’t move at all.”
One witness told City News that the driver, who he identified as a man, was driving on the kerb “hitting anything that comes in the way”.
“People, fire hydrants, there’s mail boxes being run over,” said the unnamed man, who said he was driving behind the van during the incident.
As the van continued, the man said he honked his horn to try to warn pedestrians. “I witnessed at least six, seven people being hit and flying in the air, like killed, on the street,” he said.
Toronto Mayor John Tory called it “a very tragic incident”. He said he had “offered any and all assistance that the city can provide to the police to help this investigation”.
The United States and Europe have seen an increase in driving attacks in recent years. In October 2017, a man in New York drove a van down a bicycle path, killing eight people.