ATLANTA — Two firefighters sustained minor injuries while battling a blaze that sent thick smoke into a terminal at Atlanta's airport, authorities said.

The early Tuesday morning blaze involved an escalator in Concourse T, filling the area with heavy smoke, Atlanta Fire Rescue spokeswoman Janet Ward told The Associated Press.

Passengers were re-routed to other concourses at Hartsfield-Jackson Atlanta International Airport, the world's busiest airport.

Ward said two firefighters were hurt when they slipped in water. They were not hospitalized, authorities said, and there were no reports of any other injuries.

Crews responded to calls reporting smoke in the area around 5:20 a.m., airport spokesman Reese McCranie said. The fire involved an escalator that connects the concourse to a lower level where passengers board The Plane Train, which connects the terminals, McCranie said.

By 7 a.m., all gates were operational and all flight operations were normal, McCranie said.

"The train is running to other concourses, it's just not stopping at Concourse T," he said.

Passengers can walk to the concourse when the train is not running.

The airport was already busy with holiday travel after the Labor Day weekend, McCranie said. He said passengers should allow extra time to get through security and get to their gates as authorities investigate what caused the fire.

"At this time, we believe that it may have started from a motor in one of the escalators," airport officials said in a statement shortly after 11 a.m.