Heathrow Airport in London has been closed following a significant fire at a substation, which resulted in a power outage impacting the airport's operations.

The incident occurred late Thursday evening, around 2300 GMT, as large flames and heavy smoke were observed emanating from the substation.

This is one of Europe’s busiest airports and the fifth busiest in the world, and the closure has stranded passengers globally, raising concerns among airlines regarding the integrity of vital infrastructure.

Emergency responders reported that the fire led to a major blackout affecting the airport's electrical systems, including backup power supplies.

While the cause of the fire remains undetermined, the fire department indicated that it involved approximately 25,000 liters of coolant oil within the substation.

Firefighters managed to control the blaze by early Friday morning, utilizing white foam to extinguish the flames.

The police have stated that there is currently no indication of criminal activity related to the fire, although counter-terrorism officers will lead the investigation due to the critical nature of the airport's infrastructure.

The last time a European airport experienced disruptions on such a large scale was during the volcanic ash crisis in Iceland in 2010, which led to the cancellation of nearly 100,000 flights.

The current situation is expected to impose significant financial repercussions on the aviation sector, with potential losses amounting to tens of millions of pounds, alongside the risk of disputes over liability.

On the day of the incident, Heathrow had scheduled 1,351 flights, which were expected to carry up to 291,000 passengers.

As a result of the closure, numerous flights were redirected to other airports across the UK and Europe, and many long-haul flights returned to their points of origin.

Airlines are now tasked with urgently reorganizing their networks to manage the rerouting of aircraft and crew.

In the vicinity of Heathrow, hotel prices surged, with bookings for rooms being reported at 500 pounds (approximately $645), close to five times the usual rates.

Heathrow Airport advised travelers against heading to the airport and instructed them to contact their airlines for further information.

They indicated that the airport would remain closed at least until midnight Friday.

A spokesperson noted the uncertainty regarding when electrical services would be fully restored, anticipating significant disruptions in the coming days.

Ownership of the airport includes French firm Ardian, Qatar Investment Authority, Saudi Public Investment Fund, and several other investors from Australia, China, and Spain.

The power outage also impacted several homes and businesses across London, including data centers and logistics warehouses.

Flight tracking service showed that at least 1,350 flights to and from Heathrow were affected, including multiple cancellations from U.S. cities.

Passengers reported sporadic power restoration within the airport, as electricity returned to Terminal 4 by Friday afternoon.

However, prior to this, both Terminals 2 and 4 were completely dark due to the outage caused by the fire.

The national grid operator stated it had achieved a 'temporary solution' to restore power to all customers, including Heathrow, although it remains unclear if full electrical service has been reinstated.

The Metropolitan Police reiterated that there are no indications that foul play contributed to the fire that led to Heathrow's closure, with counter-terrorism units investigating due to the fire's impact on critical national infrastructure.

Heathrow Airport is a pivotal hub for international travel, recording January as its busiest month ever earlier this year, with over 6.3 million passengers, a marked increase of over 5% year-on-year.