Hundreds of people were stranded at King's Cross station as trains were delayed and cancelled.
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 Midlands, the South East, South West and North East of England, and Wales. British Broadcasting Corporation reports.
Hundreds of people were stranded at King's Cross station as trains were delayed and cancelled.
Traffic lights in some areas also 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 and remained so for most of the evening.
Passenger Zoe Hebblethwaite said the situation outside the station was "absolute mayhem" and that passengers "couldn't find an assistant to speak to".
The BBC's Emma Petrie said there was an announcement asking passengers to leave the station.
By 21:00 BST, more than 1,000 passengers appeared to be stranded at King's Cross, with London North Eastern Railway and National Rail advising customers against all travel for the rest of the day.
Later on, some LNER trains were running southbound into King's Cross, and services to Stevenage and Peterborough from London also resumed, but not further up the East Coast Main Line.
One passenger told BBC Radio 5 Live her train took nearly 13 hours to reach London King's Cross from Edinburgh - a journey which would normally take less than five hours.
"By hour seven things were starting to get pretty tense," Dayna McAlpine said. "We were being held in the middle of nowhere. Food ran out about five hours ago... We quite simply had to sit."
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.