Ontario Provincial Police say all eastbound express lanes on Highway 401 approaching Yonge Street have reopened after closure due to a serious collision Thursday.
Emergency services were called to the scene just before 1 p.m. after a transport truck struck a woman.
Toronto paramedics said the victim was taken to hospital in critical condition.
The transport truck driver remained at the scene.
Police said they are trying to determine why the woman was in a live lane of traffic on the highway. In an update Thursday evening, police said officers are also still trying to identify the woman, described as 30 to 40 years old, and asked for assistance from the public.
Eastbound express lanes were closed in the area and traffic was diverted following the collision.