Six fire engines and around 40 firefighters were called to a fire at a house on Weighton Road in Harrow.
Half of the ground floor, a large part of the first floor and the whole of the roof were destroyed by fire in the two floored house.
One man and one woman were treated on scene by the London Ambulance Service and were taken to hospital.
The Brigade was called at 1657 and the fire was under control by 1921. Fire crews from Northolt, Mill Hill, Stanmore, Hendon and Harrow fire stations were at the scene.
The cause of the fire is believed to be accidental and due to an electrical fault.