Four fire engines and around 25 firefighters tackled a fire at a flat on Thurlow Street in Walworth.
Part of a derelict flat on the fourth floor of a residential block was damaged by fire. There were no reports of any injuries.
The Brigade was called at 0328 and the fire was under control by 0418. Fire crews from Old Kent Road, Peckham, New Cross and Lambeth fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.