Four fire engines and around 25 firefighters tackled a flat fire on King Henry's Road in Primrose Hill.
Part of a ground-floor flat was damaged by fire. Firefighters led five people to safety from the building and a further 20 people were out of the building before the Brigade arrived. One man was treated on scene by London Ambulance Service crews after suffering from smoke inhalation.
The Brigade was called at 1906 and the fire was under control by 2010. Fire crews from Euston, Kentish Town and West Hampstead fire stations attended the scene.
The fire is believed to have been accidental and caused by an electrical fault within a consumer unit.