Twenty three people were sent to hospital after a double decker bus collided with a tractor trailer, just northeast of Cornwall.
The crash happened in the westbound lanes of the highway at around 2:30 p.m., near the Quebec border.
OPP say an adult female (previously reported as a male teen) was airlifted with life-threatening injuries and three other passengers were rushed to hospital with serious injuries.
About 19 passengers sustained minor to moderate injuries and were taken to hospital.
About 45 passengers were on board the double-decker MegaBus, which was travelling from Montreal to Kingston.
Non-injured passengers were transported to the Williamstown arena.