A small alligator found under an escalator at Chicago's O'Hare international airport has left authorities puzzled.

A maintenance worker discovered the alligator, which is about a foot (30cm) long, on Friday in Terminal 3, said the Chicago police spokesman Jose Estrada. An officer captured the reptile by putting a rubbish bin over it. No one was injured.

"We don't know where it came from or how long it'd been residing in the airport facilities," Estrada said. "It's one of those random incidents."

The gator is being cared for by the Chicago Herpetological Society. "It was in pretty bad shape," said Jason Hood, the group's president. "We're trying to get it healthy and find a place for it."

He said the gator would probably be taken to an out-of-state alligator farm once authorities gave the organisation the all-clear to release it.