An 86-year-old  woman is dead and 10 other people including three children are injured after a multi-vehicle collision on Highway 401 near Leslie.

Ontario Provincial Police said four vehicles were involved.

Toronto paramedics say a woman was transported with life-threatening injuries to a hospital, where she was pronounced dead.

Police said 10 other people suffered non-life-threatening injuries.

The cause of crash is unknown.

All westbound express lanes on Highway 401 were closed at Warden Avenue for the investigation but have since reopened.