Parts of Soho and Piccadilly have been plunged into darkness, surprising commuters and tourists.
One witness described the scene as “mayhem”, while others took photos of the unusually dark streets.
UK Power Networks Tweeted: “Engineers are on their way to site and we expect to have power restored within 2 hours at present.”
Christmas lights, traffic lights and Piccadilly’s electronic advertising billboards have all lost power in the outage.
Bars, retaurants and shops have also been struck.
Another joked: “Piccadilly Circus taking #blackfriday to new levels with major power cut”
A third said: “You can’t see where you are walking throughout Soho, Shaftesbury Avenue, Piccadilly Circus and Chinatown.