Four fire engines and around 25 firefighters were called to a fire at an office block on North Circular Road in Park Royal.
An office on the first floor of a nine-storey building was destroyed by the fire. There were no reports of any injuries.
The Brigade's 999 Control Officers took 18 calls to the visible blaze.
The Brigade was called at 1904 and the fire was under control by 2029. Fire crews from Willesden, Ealing, North Kensington and Chiswick fire stations were at the scene.
The cause of the fire is under investigation.