Six fire engines and 35 firefighters and officers were called to a fire at a house converted into flats in Eton Avenue in Hampstead.
Part of a flat on the third floor of the building and part of the roof of the building were damaged by fire.
The Brigade was called at 1013 and the fire was under control at 1207. Fire crews from West Hampstead, Kentish Town, Euston and Soho fire stations attended the scene.
The cause of the fire is believed to be accidental and due to the failure of an electric downlighter.