Power cuts at the heart of London's West End have left thousands of people without electricity on one of the hottest days of the year.
The giant illuminated signs in Piccadilly Circus went out
Businesses have been urged to switch off air conditioning, Oxford Circus Tube station had to shut and tills and lights went off in shops.
Power is being cut off in different parts of Soho for four hours at a time.
Energy supplier EDF said four faults had hit the network, compounded by high demand for air-conditioning.
Power has been rationed and there were three scheduled four-hour power cuts starting with Carnaby Street in the morning.
Some of the affected companies evacuated their buildings because it was becoming too hot inside, and many employees went home.
Piccadilly Circus's giant illuminated signs and traffic lights went out, and Oxford Circus Tube station was forced to close for an hour at lunchtime.
The station re-opened thanks to London Underground's back-up supply, a Transport for London spokesman said.
EDF said its emergency teams would work through the night to fix the problem - caused by faults at two substations, and on two underground cables.
Thirty EDF vehicles are in the area, advising customers.
"We do understand how much disruption these interruptions have caused but stress this is a highly unusual sequence of faults, " a spokesman said.
"Our emergency teams are doing everything possible to restore normal supplies as soon as they can."
He added that the faults were not thought to be weather related, but things had been made worse by the high demand on the power network due to the hot weather.
Jace Tyrrell, of the New West End Company, which represents businesses on Oxford Street and Regent Street, said it was too early to say how much the blackouts had cost shops.
"This is bad news for business and bad news for shoppers in the West End," he said.
"We are very disappointed on behalf of businesses. It is even more disappointing for shoppers who turn to stores to escape the heat."
The rolling power cuts could be repeated on Friday if the problem is not fixed overnight.
They come just three days after EDF announced its second raft of price hikes this year.
From Monday it will charge 19% more for gas and 8% more for electricity - rising to 9.1% for customers in its northern region.
The energy giant blamed the increases on soaring wholesale fuel costs.