A 28-year-old woman, of Oshawa, is dead after a multi-vehicle crash on Highway 401 near Pickering.
It happened in the westbound lanes of the highway near Whites Road at around 11 a.m.
Ontario Provincial Police (OPP) say all other drivers involved sustained minor injuries.
There are no signs of impaired driving and no charges have been laid, police say.
The OPP say that all westbound collectors lanes are currently closed at Whites Road as a result of the collision.
The circumstances surrounding the crash remain unclear.