Six fire engines and around 40 firefighters were called to a fire at a building on Coventry Street in Soho.
The basement of a seven-storey building was damaged by the fire. Around 75 people were evacuated from a hotel above as a precaution. Two people were assessed on scene for smoke inhalation by London Ambulance Service crews.
The Brigade's fire investigators believe the fire was caused by the unsafe disposal of smoking materials.
Station Commander Emma Carr, who was at the scene, said: "The fire was in the basement of a seven-storey commercial building and crews worked hard to bring the fire under control.
"We had to evacuate around 75 people as a precaution due to smoke spread.
“It's believed this fire was caused by unsafely discarded smoking materials. 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."
The Brigade was called at 0148 and the fire was under control by 0303. Fire crews from Soho, Euston, Lambeth and Dowgate fire stations were at the scene.