Two crews from Cambridge, one from Sawston, and one from Suffolk attended a bus fire on the A11 Northbound between Balsham and the junction to the Wilbrahams.
Firefighters wearing breathing apparatus used two hose reels to extinguish the fire on the double decker bus which was well alight on a slip road.
Cause was accidental, by equipment, with a fire that started in the engine.
Crews returned to their stations by 2.56pm.