Dufferin OPP, Orangeville Fire Department and Dufferin paramedics responded to a serious three vehicle collision on Highway 10 north of Mono Centre Road.
An occupant of one of the vehicles involved was airlifted to a Toronto trauma centre with life-altering injuries.
Three other people were taken to hospital with non life-threatening injuries.
Highway 10 between Sideroad 20 and Mono Centre Road was closed for several hours while police investigated.
Witnesses of the collision are asked to contact Dufferin OPP.
