Some flights at Heathrow are due to resume later today as the airport targets a return to normal operations on Saturday.
The London hub experienced a “significant power outage” this morning following a fire at a local power station.
In an update issued this afternoon, the airport said some flights would take off later today, with the first being repatriation flights and to relocate aircraft.
The statement read: “Our teams have worked tirelessly since the incident to ensure a speedy recovery.
“We’re pleased to say we’re now safely able to begin some flights later today. Our first flights will be repatriation flights and relocating aircraft.”
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The statement encouraged passengers not to travel to the airport “unless your airline has advised you to do so”, adding Heathrow would now work with affected airlines on repatriating passengers who were diverted to other airports across Europe.
It continued: “We hope to run a full operation tomorrow and will provide further information shortly. Our priority remains the safety of our passengers and those working at the airport.
“As the busiest airport in Europe, Heathrow uses as much energy as a small city, therefore getting back to a full and safe operation takes time.
“We apologise for the inconvenience caused by this incident.”
Aviation analytics firm Cirium estimated that airlines had been scheduled to operate 665 flights from Heathrow today, equating to more than 145,000 seats.
A further 669 flights were due to arrive, representing 145,836 seats.
For Saturday, there are 615 flights scheduled to depart from Heathrow, with 136,951 seats, while 604 flights are scheduled to depart from the airport, with 134,726 seats.
A BA spokesperson said: “We’ve been given clearance by Heathrow airport to depart eight of our long-haul flights today from 7pm.
“We are now urgently contacting customers to let them know so they can make their way to the airport from 5pm.
“We thank all of our customers for their patience and continue to ask them to keep checking ba.com for the latest flight information.”