Eight fire engines and around 60 firefighters were called to a fire at a derelict building on Horsenden Lane South in Perivale.
The roof and the first floor of a row of derelict terraced flats were alight. There are currently no reports of any injuries.
Station Commander Justin Randtoul, who was at the scene, said: “Firefighters worked hard to bring the blaze under control and are expected to remain on site throughout the evening.
"The fire was generating significant smoke, and we strongly advised local residents and businesses to keep windows and doors closed.
"Please continue to avoid the area wherever possible, as road closures are in place and are causing congestion.”
The Brigade's Control Officers took the first of 15 calls to the fire at 1758 and sent crews from Wembley, Chiswick, Ealing and surrounding fire stations to the scene. The fire was under control by 1946.
The cause of the fire is under investigation.