Four fire engines and around 25 firefighters tackled a small fire underneath a substation on Dean Street in Soho.
There were no reports of any injuries.
The fire is believed to have been accidental and caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: “If you're 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 1457 and the fire was under control by 1626. Fire crews from Soho, Euston, Lambeth and Islington fire stations attended the scene.