Toronto police say that they were called to the scene shortly after 11 a.m.
The motorcyclist suffered serious injuries. He was unconscious and bleeding when transported to hospital, police say.
Earlier in the morning, a teenage male was struck by a vehicle at York Mills Road and Sandover Drive.
The male was taken to hospital with non-life threatening injuries.
York Mills Road was closed in both directions for about two hours as police investigated the collision.