A 30-year-old woman was airlifted to a Toronto hospital late Wednesday afternoon.
Police say she suffered life-threatening injuries in a collision on Penetanguishene Road near Horseshoe Valley Road.
Two children were taken to Royal Victoria Regional Health Centre as a precaution.
The collision happened just before 4 p.m. Penetanguishene Road was closed for several hours while police investigated.
Witnesses are asked to call the OPP at 1-888-310-1122.