LONDON, UK — Britain’s Heathrow Airport was closed all day Friday after a fire at a nearby electrical substation knocked out its power, disrupting flights for hundreds of thousands of passengers at Europe’s busiest travel hub.

At least 1,350 flights to and from Heathrow were affected, flight tracking service FlightRadar 24 said, and the impact was likely to last several days as passengers try to reschedule their travel.

Some 120 flights were in the air when the closure was announced, with some turned around and others diverted to Gatwick Airport outside London, Charles de Gaulle Airport in Paris or Ireland’s Shannon Airport, tracking services showed.

Lawrence Hayes was three-quarters of the way to London from John F. Kennedy International in New York when Virgin Atlantic announced they were being diverted to Glasgow.

“It was a red-eye flight and I’d already had a full day, so I don’t even know how long I’ve been up for,” Hayes told the BBC as he was getting off the plane in Scotland. “Luckily I managed to get hold of my wife and she’s kindly booked me a train ticket to get back to Euston, but it’s going to be an incredibly long day.”

The fire at a power station about 2 miles from the airport was brought under control about seven hours after it erupted in a ball of flames, the London Fire Brigade said.

“We don’t know the cause of this fire. It’s obviously an unprecedented event,” Energy Secretary Ed Miliband said.

Miliband said the fire had also knocked out a backup power supply to the airport. Heathrow said in a statement that the fire had given it no choice but to close the airport for the day.

“We expect significant disruption over the coming days, and passengers should not travel to the airport under any circumstances until the airport reopens,” the airport said.

Heathrow is one of the world’s busiest airports for international travel. It had its busiest January on record earlier this year, with more than 6.3 million passengers, up more than 5% from the same period last year. January also was the 11th month in a row that it averaged over 200,000 passengers a day, with the airport citing trans-Atlantic travel as a key contributor.

The disruption was reminiscent of the 2010 eruption of Iceland’s Eyjafjallajokull volcano, which spewed clouds of ash into the atmosphere and created trans-Atlantic air travel chaos for months.

Heathrow was at the heart of a shorter disruption in 2023 when Britain’s air traffic control system was hit by a breakdown that slowed takeoffs and landings across the U.K. on one of the busiest travel days of the year.

Anita Mendiratta, an aviation consultant, said the impact of the closure will be felt over two to four days as airlines, cargo carriers, and crews are re-mobilized and passengers rebooked.

“As soon as the airport opens up at midnight tonight, it’s not only about resuming with tomorrow’s flights, it’s the backlog and the implications that have taken place,” Mendiratta said. “Crew and aircraft, many are not where they’re supposed to be right now. So the recalculation of this is going to be intense.”

United Airlines said seven of its flights returned to their origin or diverted to other airports and its flights Friday to Heathrow were canceled.

At least two flights from Taiwan to London were affected, the island’s Central News Agency reported. A China Airlines flight that left in the morning turned around and was headed back to Taiwan. An EVA Air flight stopped in Bangkok, a planned stopover, while the airline assessed the situation in London.

Singapore Airlines said on the X social media platform that its overnight flight to London was diverted to Frankfurt.

The FlightAware website showed more cancellations, including two from JFK in New York, a Delta Airlines flight and an American Airlines flight.

National Rail canceled all trains to and from the airport.

The London Fire Brigade sent 10 fire engines and around 70 firefighters to control the blaze after flames soared into the sky when a transformer at an electrical substation caught fire in west London late Thursday night.

About 150 people were evacuated from their homes near the power station.

“This was a very visible and significant incident, and our firefighters worked tirelessly in challenging conditions to bring the fire under control as swiftly as possible,” Assistant Commissioner Pat Goulbourne said. “Thanks to their efforts and coordinated multi-agency response, we successfully contained the fire and prevented further spread.”

Scottish and Southern Electricity Networks said in a post on X the power outage affected more than 16,300 homes.

Heathrow normally opens for flights at 6 a.m. due to nighttime flying restrictions. It said the closure would last until 11:59 p.m. Friday.

The U.K. government earlier this year approved building a third runway at the airport to boost the economy and connectivity to the world.