One person was airlifted to hospital in a two-vehicle crash on Highway 40 in St. Clair Township.
Lambton OPP, Lambton EMS, the St. Clair Township Fire Department and Ornge Air Ambulance responded to the collision at around 1:45 p.m. Thursday.
Police said a pick-up truck and transport collided head-on on Highway 40, just south of Oil Springs Line.
The driver of the pick-up, a 46-year-old from Welland, was airlifted to hospital with what police said were life-threatening injuries. The driver of the tractor-trailer was not hurt.
The highway was closed to traffic between Courtright Line and Bickford Line until about 3 a.m. Friday.
Lambton OPP, along with the West Region Traffic Incident Management and Enforcement (TIME) Team continue to investigate.
Anyone with any information about the crash is urged to call Lambton OPP at 1-888-310-1122.
With files from Natalia Vega