A plane takes off over a road sign near Heathrow Airport in London, June 5, 2018. (AP Photo/Kirsty Wigglesworth, File)

LONDON (AP) — Britain's Heathrow Airport will be closed Friday after an electrical substation fire knocked out its power, potentially affecting hundreds of thousands of passengers who use one of Europe's biggest travel hubs.

Thousands of homes also lost power and about 150 people had to be evacuated after a transformer within an electrical substation caught fire in west London.

"To maintain the safety of our passengers and colleagues, we have no choice but to close Heathrow" for the full day Friday, the airport's statement said. "We expect significant disruption over the coming days, and passengers should not travel to the airport under any circumstances until the airport reopens."

It said it will provide an update on its operations when it has more information on restoring power available.

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.

London Fire Brigade said 10 fire engines and around 70 firefighters were on the scene of the fire, which started late Thursday night.

Footage posted to social media showed huge flames and large plumes of smoke coming from the facility.

"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," Assistant Commissioner Pat Goulbourne said.

Scottish and Southern Electricity Networks said in a post on X the power outage affected more than 16,300 homes.

Emergency services were called to the scene at 11.23 p.m. Thursday. The cause of the fire is yet to be determined.

Goulbourne urged people to take safety precautions and avoid the area as crews worked to extinguish the blaze.

The website FlightAware showed cancelations of several flights to Heathrow, including two from John F. Kennedy International in New York, a Delta Airlines flight and an American Airlines flight. A United Airlines flight from Washington Dulles International also was cancelled.

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.