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.

More than 1,300 flights were affected after a fire at a nearby electrical substation. Hundreds of thousands of passengers were stranded around the world.

Flight schedules around the world have been thrown into disarray by a massive fire raging at an electrical substation near London Heathrow Airport. The fire wiped out power at the world’s fifth-busiest airport and also knocked out its back-up power system.