Flights at the United Kingdom’s Heathrow Airport have resumed after a fire knocked out its power supply and shut Europe’s busiest airport for the day, throwing the plans of tens of thousands of travellers into chaos.

London’s main airport said late on Friday that its teams had worked tirelessly to reopen after it suffered a power failure due to a fire at an electrical substation supplying the facility.

The flight-tracking website FlightRadar24 earlier said the closure would affect at least 1,351 flights.

Heathrow said there would be a limited number of flights on Friday, mostly focused on relocating aircraft and bringing planes into London.

“Tomorrow morning, we expect to be back in full operation, to 100 percent operation as a normal day,” Heathrow Chief Executive Thomas Woldbye said. “What I’d like to do is to apologise to the many people who have had their travel affected. … We are very sorry about all the inconvenience.”

Counterterrorism officers from the Metropolitan Police are leading the investigation into the cause of Thursday night’s fire. The force said there was “no indication of foul play” but “we retain an open mind at this time.”

The London Fire Brigade later said police believed the fire to be nonsuspicious.

Heathrow is one of the most globally connected airports and regularly ranks among the top five busiest gateways worldwide.

The airport serves more than 200 destinations in nearly 90 countries and territories and last year handled about 84 million passengers, the largest number on record.

Geoffrey Thomas, an aviation analyst, told Al Jazeera that about a quarter of a million passengers were expected to be diverted across Europe and the United Kingdom because of Friday’s shutdown.

“There’s going to be mayhem for 24 hours, or probably more like 48 or 72 hours. There are other airports around the United Kingdom that do handle the diverted flights, but their ability to handle this number would be very problematic,” he said.

“So a lot of these flights would divert into Europe. But there again, the problem for airlines is, all of a sudden, you’ve got a flight in Frankfurt where it’s supposed to be in Heathrow, you’ve got crew that are in the wrong place. It’s a chaotic situation,” Thomas added.

Ellen, a traveller from the British county of Surrey, was planning to fly to Venice on Friday on British Airways but had to change her trip due to the shutdown.

“We were supposed to fly to Venice this morning from Heathrow for a day trip for my 30th birthday present. It was a surprise booked by my cousin for the two of us. We have been offered a full refund by the airline so won’t be travelling now this weekend but will try to rearrange for another weekend soon,” she told Al Jazeera.

Lloyd, 34, said he was planning to travel from the Scottish city of Glasgow to the United States via Heathrow to visit his partner but he received an email while he was still en route to Glasgow Airport on Friday morning informing him that his 6:35am flight had been rebooked to a later time and to a different US airport.

By the time he got to the airport, his flight had been cancelled and he was advised not to travel to Heathrow. While disappointing, he said, it was better than being stuck at the London airport.

Footage shared on social media showed an inferno several storeys high, lighting up the night sky and emitting huge plumes of black smoke.

The London Fire Brigade said it had deployed 10 engines and about 70 firefighters to a fire at an electrical substation near the airport in Hayes, west London, and brought the blaze under control.

“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 multiagency response, we successfully contained the fire and prevented further spread.”

[Aljazeera]