Four fire engines and around 25 firefighters tackled a fire on Old Bond Street in Mayfair.
An electrical apparatus unit in the basement of a four storey building, made up of a shop and offices, was destroyed by fire. Around 35 people left the building before firefighters arrived. Three people from the second floor were led to safety by firefighters wearing breathing apparatus and assessed at the scene by London Ambulance Service crews.
The Brigade was called at 1230 and the fire was extinguished by 1614. Crews from Soho, Euston and North Kensington fire stations attended the scene.
The fire is being treated as accidental and is believed to have been caused by an electrical fault.