PITTSBURGH — A 2-year-old boy visiting the Pittsburgh zoo was killed Sunday morning when he fell off a railing that his mother had put him on top of to view a pack of African painted dogs, who pounced on the child and mauled him, police said.

It was not clear whether the boy died from the fall into the wild dog exhibit area or from the attack, said Barbara Baker, president and CEO of the Pittsburgh Zoo & PPG Aquarium.

“It was very horrific,” said Lt. Kevin Kraus, of the Pittsburgh police, who added that the dogs attacked “immediately” after the boy fell. Zoo officials at first estimated the boy fell 14 feet, but police said it was 11.

When the boy fell, other visitors immediately told staff members, who responded along with Pittsburgh police. Zookeepers called off some of the dogs, and seven of them immediately went to a back building. Three more eventually were drawn away from the child, but the last dog was aggressive and police had to shoot the animal, officials say.

The zoo was immediately closed; it was not clear when it would be reopened, authorities said. Authorities didn’t immediately release the name of the boy or his mother, but say she is 34 years old and lives in Pleasant Hills, just outside Pittsburgh. The boy’s father arrived on the scene soon after the accident, police said.

The dogs are about as big as medium-sized domestic dogs, 2 to 21/2 feet high and 37 to 80 pounds, according to the zoo. The dogs hunt in packs in the wild, and Baker said that they “were in pack mentality” during the attack.

The dogs normally live in a 1.5 acre exhibit that’s part of a larger open area where elephants, lions and other animals can be seen. Visitors walk onto a deck that is glassed on the sides, but open in front where the railing is located. Visitors can look out at the dogs below. Zoo officials said there is also a mesh barrier beyond the railing, but Kraus said it was designed to catch small objects, such as cameras, and not humans.

Baker said the Pittsburgh Zoo has never had a visitor death. She said no decision has been made yet on the future of the exhibit.