Ontario Provincial Police officers at the Leeds detachment responded to the scene of the crash at about 11:30 a.m. Saturday.
Police said the driver of a black Pontiac Sunfire hit some snow, lost control then hit a light standard near Mallorytown, Ont. Several other vehicles also entered the ditch in that area immediately after.
Police said a double-decker bus hit the cars and overturned at the Long Beach exit. Police estimated there were seven vehicles involved in the crash.
There were 11 people taken to hospital including some of the 49 people who were on the bus at the time of the crash. No serious injuries were reported.
Traffic was backed up for several hours on Saturday and police continue to investigate.