A power cut has plunged parts of central London into darkness.
It has hit the busy Soho entertainment district, which is packed with tourists, Black Friday shoppers and people out to enjoy the nightlife.
UK Power Networks said that "engineers are now on site" and have started investigations in to the cause of the blackout.
People at the scene posted images on social media of darkened streets, and Piccadilly Circus with many of its famous lights extinguished.
Theatregoers heading for the West End performance of Aladdin the Musical were told it had been cancelled.
A spokesman for the Disney West End musical, playing at the Prince Edward Theatre, tweeted: "Due to the ongoing power cut in Central London we regret that tonight's performance has been cancelled. Tickets will be refunded. Please refer to your original point of purchase for full details. We regret any disappointment or inconvenience caused by this unavoidable occurrence. Thank you."
The power cut meant that the bright lights of billboards in the West End went out, while rush hour commuters and office workers found themselves in darkness.
Passer-by Adrie van der Luijt tweeted: "You can't see where you are walking throughout Soho, Shaftesbury Avenue, Piccadilly Circus and Chinatown. Astonishing. No traffic lights."
Transport for London said the Tube network has not been hit by the powercut but that travellers had been held at the stations such as Tottenham Court Road and Oxford Circus to prevent overcrowding.
UK Power Networks later tweeted that e ngineers had been able to get some power back on to the area by re-routing around the fault. Engineers estimated that power would be back on between 8.30 and 9.30pm.
At Piccadilly Circus in central London the world-famous TV advertising hoarding was temporarily affected before partially starting to work again at around 7.30pm.
Some shops on Regent Street were also left in the dark as thousands of people tried to get their hands on Black Friday bargains, though many stores appeared unaffected. Christmas lights strung across the roads and traffic signals were also still working.
Kurt Pollington, 56, who works for a steel company on nearby Bond Street, said: "I was on the bus down Piccadilly from Oxford Circus and half way down all the shop lights were out.
"Shoppers were leaving the stores and they just had emergency lights on. I got off just past the Cafe Royal and the shops on the left were all out.
"The famous Piccadilly neon lights were completely black and out and most of Chinatown was as well."
Mr Pollington said the power cut had caused gridlock around Shaftesbury Avenue, leaving a "weird atmosphere".
He said: "The lights were out in Regent Street - you can imagine the crossroads, it was all for one and one for all.
"A couple behind me on the bus were saying it was ironic that it was Black Friday and that the shops were all blacked out."
Both Scotland Yard and the London Fire Bridge said they were "aware" of the power cut but had not been called out to any particular incidents.
Despite the eerie scenes some people were pleased that their night out had not been ruined.
Theatregoer Sarah Ellacott said "the power came back to a rapturous applause" at the performance of Harry Potter And The Cursed Child.