Ontario Provincial Police say snow was falling, the road was slick and visibility reduced when about 70 vehicles collided yesterday 80 kilometres east of Toronto near Newcastle.
It happened around 3 p.m. and littered a one kilometre stretch of highway with mangled metal.
Five people were transported to local hospitals, two in serious condition.
One was later flown to Toronto`s Sunnybrook Hospital, but OPP spokeswoman Constable Linda Wolf said none of the injuries was life-threatening.
The chain reaction wreck shutdown a 10 kilometre stretch of the highway`s east-bound lanes until nearly 10:30, and the west-bound lanes until shortly before midnight.
Dozens of people were left stranded in the cold for hours.
Wolf says buses were enlisted to take people from the crash site to a recreation centre in Newcastle where they were interviewed by police before being returned to their vehicles.
Due to the number of vehicles involved, Wolf says the investigation into the crash is likely to take several days.
And while weather conditions are certainly being looked at as a possible factor, Wolf says the crash clearly demonstrates the need for motorists to slow down and take extra care in dodgy driving conditions.