Police say a white van mounted a pavement and struck pedestrians before fleeing the scene.
The vehicle was located several streets away and the driver was arrested and taken into custody, according to local media reports.
Toronto Police confirmed the fatalaties on Twitter.
A tweet read: “Acting Chief Peter Yuen: 9 people dead, 16 people injured. One man in custody, after incident involving vehicle on Yonge Street.
“It is anticipated that investigators will be on scene for several days. There will be road closures. Beecroft Road and Doris Avenue are alternative routes. Currently North York Centre Subway Station is closed.”
Toronto’s Sunnybrook hospital confirmed it had received a number of patients and has locked down its emergency centre as an “added precaution”.
Police shut down the Yonge and Finch intersection following the Monday afternoon incident and Toronto’s transit agency said it has suspended service on the subway line running through the area.
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.
Officers initially said up around 10 people had been injured but later said it was unclear how many had been hurt or the extent of the injuries.
The incident took place at Yonge Street and Finch Avenue in the northern subrubs of Canada’s largest city, about 18 miles from the downtown area of Toronto at 1.27 ET.
No description was given of the driver, including name, age, gender or possible motive.
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.”