Four fire engines and around 25 firefighters were called to a fire in an electrical box at a block of flats on Harrow Road in Wembley.
Part of the ground floor stairwell of the three-storey block was damaged by the fire. Around 20 people left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 2110 and the fire was under control by 2201. Fire crews from Wembley, Park Royal, Willesden and North Kensington fire stations attended.
The cause of the fire is under investigation.