Flights to Heathrow Airport were delayed by up to three hours after a "technical issue" affected lighting on the runways.
The problem left some London-bound passengers stranded on the tarmac at US airports.
Twitter user Shaan Khan wrote from New York: "We are on BA116 and ground staff at JFK Airport not opening the door so we can talk to someone. Pilot growing impatient as are passengers."
Passenger Davey Hunt posted: "On the ground in Atlanta due to Heathrow light failure. The bar is open and I'm not working tomorrow so not that fussed."
— Davey Hunt (@DavidHunt82) November 7, 2018
Heathrow said the problem was resolved by 6.05am, but that customers should still check their flight status with their airline before travelling.
Nearly one in seven flights due to land at Heathrow between 6am and 8.59am were delayed by more than 15 minutes, according to figures from aviation data firm FlightStats.
This included 11 flights delayed by more than 45 minutes.
The worst delay was to a United Airlines flight from Newark, near New York, which was operating three hours and five minutes behind schedule.
Out of 64 scheduled departures between 6am and 7.59am, there was one cancellation and five flights were delayed.
Following earlier runway lighting issues both runways are now open and operational. Whilst we're continuing to monitor the situation, please check your flight status with your airlines before travelling: https://t.co/soqDdQjYT1. We apologise for the disruption to your journey.
— Heathrow Airport (@HeathrowAirport) November 7, 2018
A Heathrow spokesman said: "Our engineering teams are investigating a technical issue with the lighting system for the airport's runways.
"We have activated our contingency plans and both runways are currently open and operational, although we anticipate there will be some delays at the airport throughout this morning.
"For the latest information, passengers should check their flight status with their airlines before travelling to the airport.
"We apologise for any impact this might have on our passengers."
A spokeswoman for British Airways said: "There was an issue with Heathrow Airport's airfield lighting during the night.
"Contingency plans were quickly activated and we plan to operate our full schedule today, albeit with some delays.
"We're asking customers that are due to travel with us today to continue to monitor ba.com for any updates to their flight."