London's Heathrow Airport remains closed until midnight Friday due to a "significant power outage" caused by a fire at a nearby electricity substation, a spokesperson said.

The outage has affected the entire airport, with no clear timeline for power restoration. "To maintain the safety of our passengers and colleagues, we have no choice but to close Heathrow until 23:59 GMT on March 21," the spokesperson added.

Passengers are advised not to travel to the airport until further notice. Over 1,300 flights, including 120 already airborne, are affected, according to Sky News, citing Flightradar24, a live flight-tracking website. Some planes have been diverted to other airports, including London Gatwick Airport, those in Paris and Shannon Airport in Ireland.

British Airways, Heathrow's largest carrier, urged customers not to go to the airport until further notice and said it is working to update them on travel options.

London Heathrow, one of the world's busiest airports, handled a record 83.9 million passengers last year.

The fire that broke out in Hayes, north of the airport has also left around 16,000 nearby homes without power. The cause remains unknown, but the National Grid is working to restore electricity as quickly as possible.