Four fire engines and around 25 firefighters were called to a fire at a flat on Hodford Road in Golders Green.
A ground floor flat was destroyed by the fire. One man left the premises before the Brigade arrived. He was treated at the scene and taken to hospital suffering smoke inhalation by London Ambulance Service crews.
The Brigade was called at 0411 and the fire was under control by 0648. Fire crews from West Hampstead, Hendon and Willesden fire stations were at the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.