London's Heathrow Airport closed on Friday after a fire at a nearby electrical substation caused a power outage, airport officials said.

Heathrow, the home of airlines including IAG’s British Airways and Virgin Atlantic, handles more than 1,400 flights and 200,000 passengers a day. Some planes already en-route were diverting, including a Qantas Airways flight from Perth that is now heading to Paris, according to tracking service FlightRadar24.

A giant fire near one of the world’s busiest airports knocked out power, and the cause was under investigation. Hundreds of flights were canceled or rerouted, and analysts said disruptions could last days.