A motorcyclist is in hospital with critical injuries after a single-vehicle crash in Ajax early Sunday morning.

It happened near Harwood Avenue South and Highway 401 at around 1:45 a.m.

Durham Regional Police say the male motorcyclist, who is believed to be in his 20s, was taken to a local trauma centre for treatment.

His injuries are believed to be life-threatening.

The cause of the collision is not yet known and the area will be closed to traffic as police investigate.