Britain's Heathrow airport -- Europe's busiest -- shut down early on Friday after a major fire at an electricity substation cut power to the sprawling hub, causing disruption worldwide to hundreds of flights and thousands of travellers.

Around 120 Heathrow-bound planes were in the air when the closure was announced, according to online flight tracking service FlightRadar24.

Around 70 firefighters were deployed to tackle the "highly visible" blaze at the substation in Hayes, west London.

Videos on social media, apparently shot inside Heathrow's terminals, showed shuttered shops and deserted corridors, lit only by emergency lighting.

Heathrow, which handles more than 80 million passengers a year, has around 1,300 takeoffs or landings a day.

British Airways said the closure of its main hub "will clearly have a significant impact on our operation and our customers".

"We're working as quickly as possible to update them on their travel options for the next 24 hours and beyond," it said.

The UK's second busiest airport, Gatwick, said it would accept some flights from Heathrow.

Others were diverted to Shannon in southwestern Ireland.

"We are aware of the situation at Heathrow Airport today and are supporting as required. Flights from London Gatwick are operating as normal today," Gatwick said on X.

At least six flights were diverted from Heathrow to Shannon Airport, the Irish airport said.

Airport authorities said they "expect significant disruption" over the coming days, while flight FlightRadar24 said at least 1,351 flights to and from the airport would be affected.

"Heathrow is experiencing a significant power outage," the airport operator said on its website, adding it would be closed until just before midnight on Friday (2359 GMT).

"Passengers should not travel to the airport under any circumstances until the airport reopens," it stressed.

- Flights diverted -

London Fire Brigade was called to the "significant" blaze at Hayes in west London at 11:23 pm (2323 GMT)

It said 10 fire engines and dozens of firefighters were sent to the scene, while around 150 people had been evacuated from nearby properties.

London Fire Brigade assistant commissioner Pat Goulbourne said firefighters had worked "tirelessly in challenging conditions" and that around 8:00 am the fire had been brought "under control".

The government would be "doing everything we can" to restore power to Heathrow, Energy Secretary Ed Miliband said.

The outage left 100,000 homes without power overnight, he said, but that power had been restored to all but around 4,000.

It was "speculative" to suggest at the moment that arson might have caused the fire, the chairwoman of a parliamentary transport committee, Ruth Cadbury, said.

"There are obviously questions about it," she told Times Radio.

She said the fact the airport was dependent on one substation "does raise questions".

Other European airports, including Frankfurt, were accepting diverted flights.

In Sydney, Qantas said two flights en route to Heathrow -– a non-stop flight from Perth and another via Singapore -- had both been diverted to Paris's Charles de Gaulle airport.

Seven United Airlines flights returned to their airport of origin or to other airports and all Friday flights to London Heathrow were being cancelled, a company spokesperson said.

A Korean Air flight scheduled to depart for Heathrow from Incheon, South Korea, was delayed by 22 hours, the airline said.

- Passengers disrupted -

At Singapore's Changi Airport, a couple scheduled to fly to London told AFP they were already in the boarding area when they were notified of the cancellation.

"They told us the flight was cancelled because there's been a fire in London,” said the man, who did not want give his name.

"They booked us at a hotel and they will inform us when the next flight is available," he told AFP.

"That's all we were told."

In January, the UK government gave permission for Heathrow to build a third runway -- which could be ready by 2035 -- after years of legal disputes due to opposition from local residents.

Five major airports serve the British capital and towns nearby.

But capacity is stretched, especially at Heathrow, whose two runways each measure almost four kilometres (2.5 miles) in length.

The airport itself covers a total area of 12.3 square kilometres (4.8 square miles).

It opened in 1946 as London Airport before being renamed Heath Row after a hamlet demolished two years earlier to make way for the construction.

Situated 25 kilometres west of central London, Heathrow currently has four terminals and serves 200 destinations in more than 80 countries.

Among its main flight destinations last year were Dublin, Los Angeles, Madrid and New York.

(AFP)

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