Power has been resorted at Hartsfield-Jackson International Airport in Atlanta after an electrical fault caused a partial shut-down on Sunday evening.

Tens of thousands of passengers were delayed following the incident at the busiest airport in the world.

More than a quarter of a million people move through Hartsfield-Jackson each day, catching around 2,500 flights.

Georgia Power said personnel has worked throughout the day today to restore power at the airport as quickly and safely as possible.

“Power has been restored for all essential airport activities including all concourses and flight operations,” added a statement.

While evaluation of the incident is ongoing, the power company said it believed a piece of switchgear located in an underground electrical facility could have failed and started a fire.

This fire was located adjacent to redundant circuit cables and switching mechanisms serving the airport and those cables were damaged, resulting in the outage.

A power outage affecting Hartsfield–Jackson Atlanta Airport (ATL) has caused delays and cancellations for travel today, and may affect flights tomorrow. We are offering additional flexibility that may allow you to change your travel plans. Travel waiver: https://t.co/LxaCS8A5UU.

— United (@united) December 18, 2017

Passengers were left in darkened terminals or on-board stranded planes on Sunday evening.

More than 1,000 flights were cancelled, with delays and cancellations expected to spill on into Monday.

Flights scheduled to arrive in Atlanta from other airports are also being diverted or held at their departure airport.

Operations are expected to resume at 06:00 local time today.

A number of major airlines, including United, Southwest and American Airlines, completely suspended their operations on Sunday.

Delta Air Lines, which is based at Atlanta, said it would be forced to cancel hundreds of flights this morning.

Most of the 300 Delta cancellations Monday are early morning, inbound flights to ATL to give the operation there an opportunity to more quickly rebound. Delta’s flight schedule in ATL is expected to return to normal by Monday afternoon.

— Delta (@Delta) December 18, 2017

The fire was safely extinguished by fire crews before Georgia Power could enter the area to assess damage and begin repairs.

No passengers were in danger at any time.