Four fire engines and around 25 firefighters , including those from Stanmore, tackled a flat fire on Laleham Avenue in Mill Hill.
The Brigade confirmed that part of the ground floor of a semi-detached house converted into flats was damaged by fire. One man left the building before the Brigade arrived and was treated on scene after suffering from smoke inhalation.
London Fire Brigade was called at 2:47pm and the fire was under control by 3:40pm.
Fire crews from Mill Hill, Hendon, Stanmore and Tottenham fire stations attended the scene.
The cause of the fire is under investigation.