Six fire engines and around 40 firefighters responded to reports of a fire at a theatre on Victoria Street in Westminster.
Smoke was traced to a defective air conditioning unit on the roof. There were no reports of any injuries.
Control Officers took the call at 0220 and mobilised crews from Lambeth, Chelsea, and Soho fire stations to the scene. The fire was under control by 0522.
The fire is believed to have been caused by an electrical event within an air conditioning unit.