Four fire engines and around 25 firefighters tackled a fire on Peel Road in Wealdstone.
An area of refuse and two single-storey portable cabins were destroyed by fire. There were no reports of any injuries.
The Brigade was called at 1257 and the fire was under control by 1401. Fire crews from Stanmore, Harrow, Mill Hill and Northolt fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.