A “technical issue” affecting lighting on Heathrow’s runways early this morning could affect flights.
The airport said it was trying to fix the problem, but advised travellers to check their flight status with their airline before travelling to the airport.
Earlier passengers due to fly into Heathrow had been reporting that they had not been allowed to take off.
Flights have since been landing at the airport this morning.
Heathrow tweeted at 4.37am: “We’re currently investigating and working to fix a technical issue with the lighting system for the runways.
“Please check your flight status with your airline before travelling to the airport.
“We’re sorry for the impact this will have on our passengers.”
Heathrow later said: “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 airline before travelling.”
British Airways initially warned it was diverting some flights but subsequently said contingency plans have been activated and it plans to operate a full schedule today, albeit with some delays.