Nearly a million people have been affected by a major power cut across large areas of England and Wales, affecting homes and transport networks.
National Grid said it was caused by issues with two power generators but the problem was now resolved.
Blackouts were reported across the South East, South West and North East of England, the Midlands and Wales.
Trains were delayed and cancelled, and traffic lights in parts of London stopped working.
The Department for Transport, said: “Today’s power outage has had knock on impacts on travel.
“We’re working hard with Network Rail and others to ensure systems are up and running as quickly as possible, so that everyone can complete their journeys safely.”
At the height of the Friday rush hour, all trains out of King’s Cross were suspended.
The BBC’s Emma Petrie said there was an announcement asking passengers to leave the station.
Boards at Waterloo station showed no trains departing on any platforms.
Harriet Jackson, 26, said there was an “apocalyptic” scene on Northcote Road, in Battersea, when traffic lights cut out and cars were not stopping.
“Given it’s a Friday afternoon, it’s the last thing you want to encounter,” she said.
Passengers at Newcastle Airport said the power cut out for about 15 minutes, but Heathrow, Gatwick and Luton airports said they had not been affected.
Scott McKenzie, 31, from Cardiff, said “various alarms were going off” at Newcastle Airport.
“We were literally plunged into darkness and people were using their phones as torches to see and get around,” he added.
About 500,000 people were affected in Western Power Distribution’s area – including 44,500 customers in Wales – with power restored to them all shortly after 18:00 BST, the company said.
Northern Powergrid said 110,000 of its customers lost power between 17:10 BST and 18:00 BST, while Electricity North West said at least 26,000 people were without power in the North West.
UK Power Networks spokesman said 300,000 people were affected in London and the South East.
Network Rail said all trains had been stopped after a “power surge on the National Grid” but its signalling system had come back online.
Passengers have been warned to expect delays.
Thameslink said most of its trains were currently at a standstill between London and Bedford.
British Transport Police said it had sent officers to “several” train stations to provide assistance to travellers.
Merseyrail has cancelled several trains from West Kirby to Liverpool and has told customers to use the Water Street entrance for James Street station.
A spokeswoman for Transport for London said some traffic lights in the capital were “not working” but the scale of the problem was not yet known.
Ipswich Hospital said it had been affected by the power cut in that area, because its back-up generator had failed to work, but all issues had been resolved.