Ten fire engines and around 70 firefighters were called to a fire at a restaurant on Peel Road in Harrow.
The whole of the roof and the first floor was destroyed by the blaze. Part of the ground floor was also damaged by fire. Nineteen people left the building, uninjured, before the Brigade arrived.
The Brigade's 999 Control Officers took 34 calls to the fire.
One of the Brigade's aerial appliances was used to put water on the fire from above.
Fire crews were at the property throughout the morning damping down pockets of fire.
The Brigade was called at 0619 and the fire was under control by 0838. Fire crews from Harrow, Stanmore, Northolt, Wembley and surrounding fire stations were at the scene.
The cause of the fire has been recorded as undetermined.