Major failures in electricity supply have been reported in large areas of the United Kingdom, which affect homes and transport networks.
Blackouts have been reported throughout the Southeast, Midlands, Southwest, Northeast and Wales.
UK Power Networks said the problem was caused by a "failure in the National Grid network."
Trains have been delayed and canceled in England and Wales, while the fall in power is affecting traffic lights in London.
Passengers at Newcastle airport said the power supply was cut for about 15 minutes, but Heathrow, Gatwick and Luton airports said they had not been affected.
Scott McKenzie, 31, of Cardiff, said "several alarms were ringing" at Newcastle airport.
"We were literally mired in the dark and people used their phones as torches to see and move," he added.
UK Power Networks said: "We are aware of a power outage that affects large parts of London and the southeast."
Western Power Distribution said it was working on the issue and expects power to be restored before 18:30 BST.
Network Rail said all trains had stopped after a "power boost in the national network," but their signaling system had returned to operation.
Passengers were warned to wait for delays.
Thameslink said most of his trains were currently standing between London and Bedford.
With many people trying to make trips at the peak of Friday's rush hour, the British Transportation Police said they had sent officers to "several" train stations to assist travelers.
A spokeswoman for Transport for London said some traffic lights in the capital "did not work," but the magnitude of the problem was not yet known.
Ipswich Hospital said it was being affected by the power outage in that area, since its backup generator had not worked.
A hospital spokeswoman said the staff was working "completely" to keep patients safe.