Part of the Gardiner Expressway was closed Saturday morning after bales of hay reportedly fell off a truck along the route.
Toronto police told Global News that around 6:30 a.m. officers were forced to close eastbound lanes of the highway near Kipling Avenue.
Police said bales of hay fell off a vehicle without the driver noticing and numerous collisions were caused when people swerved to try and avoid them.
In an update later on Saturday, police said four people in total were taken to hospital. A 48-year-old man had life-threatening injuries, and three other people had non-life-threatening injuries.
Police said the investigation would include the vehicle carrying bales of hay originally.