Eight fire engines and around 60 firefighters were called to a fire at a flat on Apple Grove in Harrow.
Part of a four-roomed flat on the fourth floor of the building was destroyed by fire and a small part of the roof was also damaged by the blaze. Around 35 residents left the building before the Brigade arrived. One man was treated on scene by London Ambulance Service crews after suffering from smoke inhalation.
The Brigade's 999 Control Officers took 12 calls to the blaze.
The Brigade was called at 0821 and the fire was under control by 1001. Fire crews from Harrow, Northolt, Wembley, Stanmore and Ruislip fire stations were at the scene.
The cause of the fire is under investigation.