Crews from High Wycombe, Beaconsfield, Aylesbury and Chesham attended, along with one officer.
A single-storey barn measuring approximately 10 metres by 10 metres was destroyed by fire. One van and one car were also involved.
Firefighters used two hose reel jets and one main jet. An adjacent house sustained external damage, but the fire did not spread inside. The electricity provider attended to isolate the power supply.
Crews will remain at the scene for some time, dampening down and checking for hotspots.