Airport police evacuated Terminal 4 shortly before 6 a.m., according to Transportation Security Administration agent Nico Melendez. The terminal houses American Airlines, Southwest Airlines and US Airways.

The object turned out to be a replica grenade, but authorities still had to respond like it was the real thing.

"When you see these items we just don't know, so we have to act out of security and out of the safety of passengers," Melendez said. "So it is scary at first when you see something like that because you just don't know."

Melendez emphasized that any kind of replicas of guns, grenades or anything similar are not allowed on planes.