Four fire engines and 21 firefighters were called to a fire at a flat above a row of shops in Station Parade, Northolt Road in Harrow.
The whole of a five roomed flat on the first floor was gutted by fire. There were no reported injuries.
Station Manager David George, who was at the scene, said: "We were faced with a well developed fire on the first floor.
"Firefighters in breathing apparatus worked hard to get the fire under control and prevent it spreading to adjacent properties."
The Brigade was called at 1130 and the fire was under control at 1228. Fire crews from Northolt, Harrow, Wembley and Southall fire stations attended the scene.