The Ontario Provincial Police Essex County Detachment is currently investigating a serious on Highway 3 at Arner Townline.
A passenger vehicle and a commercial motor vehicle collided at the intersection.
The three occupants of the passenger vehicle were taken to hospital, two of them with non-life-threatening injuries and one with life-threatening injuries.
The driver of the commercial motor vehicle was not injured.
The OPP's Technical Collision Investigation is currently investigating the scene and the intersection in both directions will be closed.
Updates will be provided as they become available.
Anyone with information regarding this or any other incident is asked to call the OPP at 1-888-310-1122.