Four fire engines and around 25 firefighters were called to an outbuilding fire on Bowes Road in Southgate.
A semi-detached, derelict outbuilding was destroyed by fire. There were no reports of any injuries.
Sub Officer Daniel Burton, who was at the scene, said: “The fire was very visible, with flames reaching around 15ft high on arrival and producing heavy smoke.
“The roof of the building collapsed and crews worked through the night cutting away and damping down remaining deep-seated pockets of fire.”
The Brigade was called at 0404 and the fire was under control by 0714. Fire crews from Southgate, Hornsey, Finchley and Edmonton fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.