Britain's Heathrow Airport on Friday said it would be closed until midnight after experiencing a significant power outage due to a fire at a nearby electrical substation supplying the airport.

"To maintain the safety of our passengers and colleagues, Heathrow will be closed until 23h59 on 21 March," Heathrow Airport said in a post on X, adding that passengers are advised not to travel to the airport.

There was no clarity on when power may be reliably restored, a Heathrow spokesperson told Reuters in an email, and added they expect significant disruption over the coming days.

Eurocontrol, which manages air traffic control operations across Europe, said on its operations website that no arrivals were being allowed at Heathrow due to the power outage and there were diversion plans in place for flights.

According to flight tracking website FlightRadar24, some diversions to other airports were already occurring, with Qantas Airways sending its flight from Perth to Paris and a United Airlines New York flight heading to Shannon, Ireland.

A United Airlines flight from San Francisco was due to land in Washington, DC rather than London.

Heathrow was the world's second-busiest international airport in 2024 behind Dubai, according to travel data firm OAG.

The London Fire Brigade said its crews were tackling the fire in Hayes in west London and had evacuated around 150 people from the area as a precaution. (Reuters)