CHICAGO (CBS) — Power has been restored at Atlanta International Airport, where more than 1,100 flights were grounded Sunday when an underground fire knocked out power for 11 hours.

Travel experts have said the mess might not be straightened out for a few days.

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The fallout was still being felt across the United States on Monday, including in Chicago, where at least nine flights from O’Hare International Airport and two flights from Midway International Airport have been canceled.

Early Sunday afternoon, terminals suddenly went dark at Hartsfield-Jackson Atlanta International Airport, escalators and elevators halted, and some planes were forced to wait on the runway for hours.

Some travelers reported being stuck for seven hours without food or water.

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Thousands also slept on benches in dark terminals; on benches, baggage claim carousels, and even the floors.

Atlanta Mayor Kasim Reed said foul play is not suspected. The outage lasted more than 10 hours, grounding more than 1,100 flights on Sunday. Delta, the largest hub in Atlanta, canceled at least 300 more flights on Monday.

The outage lasted around 11 hours, but it could take several days to find flights for all the affected travelers, as most flights in and out of Atlanta this week were almost fully booked before the outage.

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The Atlanta airport routinely sees more than 75,000 travelers every day.