Four fire engines and around 25 firefighters tackled a fire at a flat on College Road in Harrow.
A studio flat on the second floor of a residential block was destroyed by fire. Firefighters rescued a woman from the second floor of the building via a ladder. She was treated on scene by London Ambulance Service crews. Around 40 further people left the building before the Brigade arrived.
The Brigade was called at 0012 and the fire was under control by 0201. Fire crews from Northolt, Harrow and Wembley fire stations attended the scene.
The cause of the fire is under investigation.