Four fire engines and 21 firefighters and officers were called to reports of visible smoke at a hotel in Blackfriars Road, Southwark.
The alarm was raised by a smoke detector sounding on the 7th floor. Hotel staff found light smoke in a communal area outside the lifts and around 250 people were evacuated from the affected and a neighbouring hotels.
Firefighters didn't find any evidence of a fire within the hotel. It is believed a vape pen was used inside the hotel by a guest and the smoke circulated the building through the ventilation system.
The Brigade was called at 0214 and the incident was over for firefighters at 0413. Fire crews from Dowgate, Lambeth, and Dockhead fire stations attended the scene.