Hundreds of thousands of passengers faced flight cancellations at Europe's busiest travel hub after a fire knocked out power to London's Heathrow Airport, forcing it to close for the day.

At least 1,350 flights to and from Heathrow were affected already, including several from U.S. cities that were canceled, flight tracking service FlightRadar 24 said.

Aviation consultant John Strickland says it will take several days for global airline travel to recover from a daylong closure of Heathrow Airport.

He said: "We're talking about several days' worth of disruption to get the planes recovered and start using them again to move planned and disrupted passengers."

Strickland compared the disruption to "a contained version of 9/11 or, to an extent, the Icelandic volcanic eruption" that shut European airspace in 2010.

"I remembered seeing on those occasions – particularly more so on 9/11 – it happened so quick and then U.S. airspace was closed, they were turning back aircraft and holding planes. That's the parallel I would make.

"Heathrow being such a busy airport and full, there's no kind of wriggle room for getting out of these kind of things."

The closure of Heathrow rippled through global aviation. The long-haul carrier Emirates in Dubai, which has London as one of its top destinations, canceled six round-trip flights to Heathrow on Friday alone.

Etihad in neighboring Abu Dhabi canceled two round-trip flights, while one flight diverted to Frankfurt, Germany. Qatar Airways said at least seven scheduled flights were "impacted," with its staff working with passengers.

A British government minister says a "catastrophic" fire knocked out a backup generator as well as the electrical substation that supplies power to Heathrow Airport.

Energy Secretary Ed Miliband told the BBC that the blaze is "unprecedented."

He said it's too early to know the cause but that lessons will have to be learned about "protection and the resilience that is in place for major institutions like Heathrow."

Hong Kong's Cathay Pacific Airways rerouted two overnight flights to Amsterdam and canceled at least two daytime flights to Heathrow, according to the flight status page on its website.

The London Fire Brigade says the electrical substation blaze closed Heathrow Airport is under control.

The fire caused a widespread power outage, affecting thousands of homes, local businesses, and disrupting thousands of flights.

LFB Assistant Commissioner Pat Goulbourne says the fire was under control just after 8 a.m.

"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," he said. "Thanks to their efforts and a coordinated multi-agency response, we successfully contained the fire and prevented further spread."

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% for the same period last year. January also was the 11th month in a row it averaged over 200,000 passengers a day, with the airport citing transatlantic travel as a key contributor.

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.

Seven United Airlines flights returned to their origin or diverted to other airports and its flights Friday to Heathrow were canceled, the airline said.

The FlightAware website showed more cancelations including two from John F. Kennedy International in New York, a Delta Airlines flight and an American Airlines flight.

Other jets were diverted to Gatwick Airport outside London, Charles de Gaulle Airport in Paris and Ireland's Shannon Airport, tracking services showed.

National Rail canceled all trains to and from the airport.

Flames soared into the sky when a transformer at an electrical substation caught fire in west London late Thursday night. The fire continued to smolder after daybreak.

Scottish and Southern Electricity Networks said in a post on X the power outage affected more than 16,300 homes. About 150 people were evacuated.The cause of the fire is yet to be determined.