Four fire engines and around 25 firefighters attended a fire on The Cross Way in Harrow.
The fire occurred in a semi-detached house that has been converted into flats. A ground-floor flat was destroyed by fire. There were no reports of any injuries.
The Brigade was called at 0350 and Control Officers mobilised crews from Stanmore, Harrow and Northolt fire stations to the scene. The fire was extinguished by 0437.
The cause of the fire is under investigation.