Four fire engines and around 25 firefighters were called to a fire at a house on Keswick Gardens, Wembley.
Half of a first floor was damaged by fire. A loft conversion was destroyed by fire.
Firefighters assisted a woman from the flat roof via a ladder. She was suffering from smoke inhalation and treated at the scene by London Ambulance Service crews. A further woman left the property before the Brigade arrived. She was taken to hospital by Ambulance crews.
The Brigade was called at 0502 and the fire was under control at 0705. Fire crews from Wembley, Park Royal, Northolt fire stations attended the scene.
The cause of the fire is under investigation.