Early Tuesday morning a van carrying nine people was struck from behind and rolled over near the town of Beamsville, in the Niagara region.
An 11-year-old boy was killed in the accident.
"The vehicle had been struck from behind by a tractor-trailer, it was white in colour, the make of it is a Volvo, and it failed to remain here at the scene and continued on," said OPP Sgt. Dave Woodford.
"We're looking for that vehicle at this time. There would be extensive damage to the right passenger side of the vehicle."
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 are not listed to be as severe.