Six fire engines and around 40 firefighters tackled a fire at an office on Green Lanes in Southgate.
Part of the ground and first floors of an office building with flats above were damaged by fire. A garden shed in the rear garden of an adjacent property was also destroyed by the blaze. There were no reports of any injuries.
The Brigade’s 999 Control Officers took 13 calls to the blaze.
The fire is believed to have been accidental and caused by the unsafe disposal of a cigarette.
A London Fire Brigade spokesperson said: "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.
“Never leave lit cigarettes unattended and make sure to stub them out properly and dispose of them carefully when you have finished smoking.”
The Brigade was called at 2150 and the fire was under control by 2330. Fire crews from Southgate, Edmonton, Tottenham, Hornsey and surrounding fire stations attended the scene.