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ATLANTA (CBSMiami) – Hartsfield-Jackson Atlanta International Airport, which is a hub for Delta Airlines, is struggling to return to normal after a power outage Sunday grounded all flights.

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A fire in an underground electrical facility was the cause of the outage, it also knocked out the airport’s back up power supply.

Travellers in the terminal were left in the dark, some pitched in to help where they could.

“So, we were literally carrying old people down the escalators and up escalators and carrying wheelchairs and my heart was racing because I’m scared for these people’s lives,” said Laura Ward.

Others just tried to get through it.

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“Once when we walked down the escalator, which was a nightmare, then we had to go through the tunnels that are pitch black. It was scary, you don’t know, someone might snatch you bags, whatever, you know, that was a nightmare,” said Rutia Curry.

Hundreds of travelers were stuck inside planes waiting for a gate.

“We sat on the tarmac for six hours, I have my five-month-old with me. Now we’re trying to get to Ft. Myers but all the flights have been canceled,” said Emily Sims.

The power was restored just before midnight but the damage was done. More than a thousand Delta flights were canceled Sunday and hundreds more on Monday, causing travel problems around the country. Aviation experts predict the ripple effect could continue through the week because there are few open seats on flights just before Christmas.

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A storm in April that grounded Delta planes in Atlanta resulted in five days of problems. Afterwards, the airline promised to improve operations to recover more quickly.