London's Heathrow Airport to resume flights after huge fire causes power outage

London’s Heathrow Airport said it will restart some flights later on Friday, after a massive fire caused a pre-dawn power outage at the global transport hub, disrupting travelers around the world and sending hundreds of thousands of people scrambling to make alternate plans.

In a statement on X, Heathrow said it hoped to return to full service by Saturday. For now, the airport urged stranded passengers not to travel there unless they have been specifically instructed to by their airlines.

Later, British Airways — the U.K. flag-carrier based at Heathrow — announced that eight long-haul flights to Singapore, Riyadh, Rio de Janeiro, Johanesburg and Cape Town had been given clearance to depart by the airport operator.

The blackout produced eerie scenes of the emptied airport — in one case, people had to haul their heavy luggage down a darkened stairwell, with only a cellphone to light the way — as stranded travelers in far-flung terminals sat and searched their phones for answers.

While the fire had been almost entirely extinguished by Friday afternoon, more than 1,300 flights and 200,000 passengers were affected by the closure.

The closure caused widespread confusion and chaos for travelers in London and around the globe. Many posted on social media after being temporarily stranded at airports worldwide after their flights were canceled.

Taylor Collier-Brown was stranded in Geneva with her hockey team on Friday after their flight to Heathrow was canceled following a skiing trip to Morzine in the French Alps.

“Eleven hockey girls with a match tomorrow can’t make it back — the whole team is in Geneva,” she told NBC News.

Six airports serve London, but Heathrow is the biggest. This year, the international hub predicts that at least 84.2 million passengers will pass through the airport, which has previously been described as the “most connected” in the world.

One of those disappointed passengers was Los Angeles-based comedian and star of “Adam Ruins Everything” Adam Conover, who was in transit to London for a stand-up gig when his flight was diverted midair.

“We were in the air for about it 90 minutes and they had just finished dinner service,” the 42-year-old comedian told NBC News in a phone interview Friday morning. “Then the captain came on and said there was a fire … we had to turn around.”

After a brief nap, the creator of Netflix’s “The G Word” said he’ll be flying to New York’s John F. Kennedy International Airport, where he faces a four-hour layover, a flight to Manchester and then a two-hour train to the British capital.

A video posted on social media showed the inside of the airport with only emergency lighting, while the fire raged at the substation responsible for the major hub's electricity.

The London Metropolitan Police’s counterterrorism unit was investigating the cause of the fire, but its spokesperson told NBC News that there was no indication of foul play.

That said, “there are questions to answer ... but our clarity right now is on this incident being appropriately dealt with,” a spokesperson for U.K. Prime Minister Keir Starmer told news agency PA News.

“This is a highly visible and significant incident, and our firefighters are working tirelessly in challenging conditions to bring the fire under control as swiftly as possible,” Fire Assistant Commissioner Pat Goulbourne said in a statement.

Goulbourne added that the fire had caused power outages at homes and businesses in the local area and was spewing out heavy smoke.

On Friday, the London Fire Brigade said that the fire involved an electricity substation with 25,000 liters of cooling oil that was on fire. Jonathan Smith, deputy commissioner with the LFB, said the fire began at 8:23 p.m. on Thursday evening (4:23 p.m. ET) and took 10 fire engines and 70 personnel to get it under control.

Firefighters evacuated 29 people from surrounding homes, and 150 more in an exclusion zone were taken to a rest center.

“Our firefighters worked tirelessly in challenging and very hazardous conditions under control as swiftly as possible,” Smith said, adding that the fire is now 90% extinguished. He did not comment on the cause of the fire.

Until the reports by the equipment owners are completed, it’s not possible to know the cause of the failure and the fire, Robin Preece of the Universtiy of Manchester said.

Oil is used to cool transformers at substations, he explained, but “if there is a catastrophic failure of a component, this can cause a big electrical spark or flashover which is extremely hot.”

This spark can set the cooling oil running through the transformer alight, causing the kind of large, unwieldy fire that brought down the substation.

“Fires like this are not common at all,” he added.

Paul Cuffe of the University College Dublin’s School of Electrical and Electronic Engineering, said that while Heathrow may have emergency electrical sources to ride out a smaller grid disruption, “processing planeloads of passengers requires Heathrow in its totality to consume a town’s worth of electricity, and the inability to meet this requirement is likely why flights had to be cancelled.”

This substation, Preece said, is one of many that supply Heathrow, though it may have serviced critical areas, leading to the airport-wide shutdown. There are enough supplies in the grid to restore power, "very quickly," he said, as engineers reroute electricty across the network on alternative paths to affected areas.

The disruption was expected to affect at least 1,351 flights set to arrive at or depart from Heathrow on Friday, according to FlightRadar24.

National Air Traffic Services, or NATS, the U.K.’s leading provider of air traffic control services, said it had “well-rehearsed plans in place which includes a requirement for aircraft to either turn back or divert to a non-U.K. airport, as well as stopping other flights at their point of departure.”

NATS added as part of the aviation industry’s “mass diversion plan,” it had been made clear to airlines that there was a limited capacity at other British airports to accommodate diversions.

Operations at other British airports did not yet appear to be heavily impacted.

NBC News Social Media Editor Fiona Day, who was at London Stansted Airport, said that “departures here are no busier than normal this morning. If anything, security was actually faster than normal.”

Chantal Da Silva, Zoe Holland, Patrick Smith, and Annie Hill reported from London. Phil Helsel reported from Los Angeles.

Jean Lee, Victoria Di Gioacchino and Ian Sherwood contributed.

This story first appeared on NBCNews.com. More from NBC News:

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