Six fire engines and around 40 firefighters tackled a fire at a shop with flats above on Ealing Road in Wembley.
A storage room on the lower ground floor was destroyed by fire. There were no reports of any injuries.
A London Fire Brigade spokesperson said: “Residents were advised to keep their doors and windows shut due to the smoke and avoid the area as there was heavy traffic congestion.”
The Brigade was called at 1653 and the fire was under control by 2002. Fire crews from Wembley, Park Royal, Northolt, Willesden and Acton fire stations attended the scene.
The cause of the fire is believed to have been electrical.