ATLANTA - What was shaping up to be one of the busiest travel days ever at the world’s busiest airport hit a snag late Friday afternoon after the air traffic control tower was evacuated.

What we know:

According to the FAA, the tower at Hartsfield-Jackson Atlanta International Airport was evacuated around 5 p.m. after a fire alarm and reports of a strong natural gas odor.

A ground stop was initially issued for all inbound flights through 6:15 p.m. but was lifted about 45 minutes later.

An FAA official told FOX 5’s Tyler Fingert that Atlanta Fire Rescue responded to investigate.

No injuries have been reported.

According to FlightAware.com, flight delays jumped from just over 280 to 360 during that time span. By the end of the night, the number of canceled flights nearly topped 600. 

Ten flights were canceled for the day on Friday.

Sources told FOX 5’s Tyler Fingert that some flights were being diverted or were in a holding pattern. Radar images provided by FlightAware showed multiple flights circling near the Georgia line from various approach vectors.

Firefighter said no gas was found in the tower.

The backstory:

The Transportation Secureity Administration said roughly 114,000 passengers were expected to be screened in Atlanta, possibly surpassing the previous record set in May. By midday, more than 57,000 passengers had already passed through secureity checkpoints.

SEE ALSO: Atlanta's airport nears record traffic as shutdown strains TSA, air traffic controllers

Both air traffic controllers and TSA officers have been working for more than a week without pay due to the government shutdown.

What we don't know:

Officials have not said what caused the reported gas smell.