A 59-year-old Ontario woman is fighting for her life after a single-vehicle crash on Highway 401 near Ajax early Tuesday morning.

Ontario Provincial Police say the driver crashed after her vehicle left the southbound lanes of Westney Road while merging onto Highway 401 east of Toronto shortly after 7 a.m.

Emergency crews treated the woman at the scene before she was rushed to hospital via air ambulance with life-threatening injuries.

The ramp from Westney Road to Highway 401 and one westbound lane on the highway are closed as police clear the scene.