The incident happened outside the Coed y Brenin mountain bike centre at about 14:00 GMT.
Emergency services attended the scene, and the road has now been reopened in both directions.
Anybody who may have information is asked to contact officers at the Roads Policing Unit.
North Wales Police said next of kin have been informed.
One person has died and another has been injured after a crash on the A470 near Dolgellau in Gwynedd.