Six fire engines and around 40 firefighters were called to a fire at a nightclub on Northampton Road in Enfield.
Part of the first floor and roof of the building were damaged by the fire. There were no reports of any injuries.
The Brigade's fire investigators believe the fire was accidental and caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: "This fire started on the balcony and spread into the roof void and is believed to have been started by a discarded cigarette.
“We’d rather you didn’t smoke at all, but if you are a smoker, it’s absolutely vital you ensure your cigarette is completely out when you’ve finished smoking it.
“If you don’t, you risk causing a fire which could not only destroy your home, but also cost you your life.”
The Brigade was called at 0528 and the fire was under control by 0654. Fire crews from Enfield, Edmonton, Chingford and Tottenham fire stations were at the scene.
Safety advice for smokers: