Major power failures have been reported across large areas of the UK, affecting homes and transport networks.
Blackouts have been reported across the South East, Midlands, South West, North East and Wales.
UK Power Networks said the issue was caused by a “failure on National Grid’s network”.
Trains have been delayed and cancelled across England and Wales, while the drop in power is affecting traffic lights in London.
Passengers at Newcastle Airport said the power cut out for around 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.
UK Power Networks said: “We’re aware of a power cut affecting large parts of London and the South East.”
Western Power Distribution said it was working on the issue and expects to have power restored by 18:30 BST.
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.
With many people trying to make journeys at the peak of Friday rush hour, British Transport Police said it had sent officers to “several” train stations to provide assistance to travellers.
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 was being affected by the power cut in that area, as its back-up generator had failed to work.
A hospital spokeswoman said staff were working “flat out” to keep patients safe.