A groundskeeper at the Los Angeles Zoo was rescued by firefighters after losing his footing and falling into a gorilla enclosure Thursday morning, officials said.

Zoo officials say the 55-year-old man was landscaping near the exhibit when he lost his footing on a planter and fell 15 to 20 feet into the moat, which had no gorillas at the time.

"The four gorillas that reside in that part of the habitat were still secure in their night quarters behind the scenes, zoo officials said in a statement.

Urban Search and Rescue members were called to the zoo about 8:30 a.m. and used ladders, ropes and a rescue litter to lift the man out. He was then placed in the back of an ambulance with a possible femur fracture and taken to Los Angeles County-USC Medical Center in fair condition.

Zoo officials say he was conscious the entire time.

"We currently don't have any information as to how the employee lost his footing and fell, but we will hold an internal investigation to look into the incident," zoo officials said.

In 1996, a 3-year-old boy fell into a gorilla den at the Brookfield Zoo in suburban Chicago. A female gorilla cradled the boy and protected him from other animals until zookeepers could rescue him.