Four fire engines and around 25 firefighters were called to a fire at a barn on Hill End Road in Harefield.
A single-storey barn in a large field was destroyed by fire. An on-site tractor was used to assist in turning over and damping down areas with remaining hot spots. There were no reports of any injuries.
The Brigade was called at 0202 and the fire was under control by 0449. Fire crews from Ruislip, Hillingdon, Harrow, Stanmore and crews from Hertfordshire Fire and Rescue Service attended the scene.
The cause of the fire is under investigation.