According to police, a van carrying nine people was rear-ended and overturned near the town of Beamsville, in the Niagara region.
An 11-year-old boy was killed in the accident.
At least two other people were taken to hospital in critical condition. The other six people in the vehicle were also transported to hospital, though their injuries were not listed to be as severe.
The white Volvo tractor-trailer fled the scene but the OPP said Thursday it was located at a repair shop in Brampton.
Police are still looking for the driver.