Fire-induced Power Outage Shutters London's Heathrow Airport

(UPI) -- London's Heathrow Airport, one of the busiest in the world, closed on Friday due to a "significant power outage," it said.

"To maintain the safety of our passengers and colleagues, Heathrow will be closed until 23h59 on 21 March," it said in a statement early Friday.

"Passengers are advised not to travel to the airport and should contact their airline for further information. We apologize for the inconvenience."

Air traffic monitor Flightradar24 reported that 120 aircraft were diverted to alternate airports. The closure, it said, would affect at least 1,351 flights.

The airport, which serves more than 82 million people a year, was submerged in darkness early Friday due to a fire at an electrical substation that supplies the British transport hub.

According to the London Fire Brigade, 10 fire engines and some 70 firefighters were dispatched to an electrical substation on Nestle Avenue in Hayes, a town in West London, where a fire had erupted late Thursday.

"Good progress" fighting the blaze has been achieved, but the fire remained uncontained Friday morning, it said in a statement.

The power outage not only affected the airport, but also a number of nearby homes and businesses, only some of which had regained power.

A more-than-600-foot cordon was established near the substation, resulting in around 150 people being evacuated, the fire brigade said. Twenty-nine people were escorted from neighbouring properties by firefighters.

Area residents are being advised to keep windows and doors closed "due to the significant amount of smoke," Assistant Commissioner Pat Goulbourne said.

"This will be a prolonged incident, with crews remaining on scene throughout the night," Goulbourne said in a late Thursday statement. "As we head into the morning, disruption is expected to increase, and we urge people to avoid the area wherever possible.

The cause of the fire was unknown. It was reported to the authorities at 11:23 p.m. local time.