Six fire engines and around 40 firefighters were called to reports of a fire in Kingsway, Wembley.
Half of the ground floor and half of the first floor of the semi-detached house was alight.
Station Commander Alan Brand, who was at the scene, said: “Crews worked hard to tackle this fire. A number of local roads are closed and there is congestion, so drivers should avoid the area if possible.”
The Brigade was called at 1359 and the fire was under control by 1637. Fire crews from Wembley, Willesden, Park Royal and Northolt fire stations were at the scene.
The cause of the fire is not known at this stage.