Four fire engines and 21 firefighters and officers were called to a fire at a shop with flats above in Kenton Road in Harrow.
Part of the ground floor shop was damaged by fire.
The Brigade was called at 0900 and the fire was under control at 0943. Fire crews from Stanmore, Harrow and Wembley fire stations attended the scene.
The cause of the fire is believed to be due to a fault in the control unit of a walk-in freezer.