Britain's Heathrow airport, Europe's busiest, was shut down early Friday after a major fire at an electrical substation supplying power to the sprawling facility west of London, officials said.

Airport authorities said they "expect significant disruption" over the coming days, with hundreds of flights and thousands of passengers affected.

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

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

London Fire Brigade said there had been a "significant" fire at a substation in Hayes, a nearby town in the London borough of Hillingdon.

Images on social media — which could not immediately be verified by AFP — showed huge flames and smoke rising from the substation. 

Other videos, apparently shot inside Heathrow's terminals, showed shuttered shops and deserted corridors, lit only by emergency lighting.

"The fire has caused a power outage affecting a large number of homes and local businesses, and we are working closely with our partners to minimize disruption," said London Fire Brigade assistant commissioner Pat Goulbourne.

He said the fire was first reported at 11:23 PM (2323 GMT).

"This is a highly visible and significant incident, and our firefighters are working tirelessly in challenging conditions to bring the fire under control as swiftly as possible," a statement said.

British utility firm Scottish and Southern Electricity Networks said on its website that an "unplanned outage" had left more than 16,000 homes without power in the area.

80 million a year

Heathrow handles more than than 80 million passengers a year and the operator says there are around 1,300 takeoffs or landings a day.

The website FlightRadar24 reported a number of diversions already, including a Qantas flight from Perth, Australia, sent to Paris, and a United Airlines flight from New York, which will land in Shannon, Ireland.

In January, the government gave permission for Heathrow to build a third runway — which could be ready by 2035 — after years of legal wrangling brought on by complaints from local residents.

Five major airports serve the capital and towns nearby.

But capacity is stretched, especially at Heathrow whose two runways each measure almost four kilometers in length, while the airport covers a total area 12.3 square kilometers.

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

Situated 25 kilometers (15 miles) west of central London, the present Heathrow serves 200 destinations in more than 80 countries, with passengers having access to four terminals.

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