Ten fire engines and around 70 firefighters were called to a fire at a flat above a shop on Broadway, West Ealing.
Part of a four-roomed flat on the second floor of the building was damaged by fire. There were no reports of any injuries.
Station Commander Colin Digby, who was at the scene, said: "The fire took hold on the roof extension above the shop and there was some smoke coming out from the edges of the building.
"Crews used one of the Brigade's 32-metre turntable ladders for elevated access. Our drone was also used along with a thermal imaging camera to check for any fire spread.
"The Broadway is closed and there are currently diversions in place. We're advising people to avoid the area whilst firefighters remain on scene this evening."
The Brigade was called at 1610 and the fire was under control by 1752. Fire crews from Ealing, Acton, Southall, Wembley and surrounding fire stations attended the scene.
The fire is believed to have been accidental and caused by hot works being carried out.