PITTSBURGH —  A mother’s attempt to give her 2-year-old son a better view of wild African dogs turned into a fatal tragedy after the boy fell into the exhibit and was attacked by a pack of the animals as relatives and bystanders looked on.

The mother had picked the child up and put him on top of a railing at the edge of a viewing deck at the Pittsburgh Zoo late Sunday morning, Lt. Kevin Kraus of the Pittsburgh police said.

“Almost immediately after that he lost his balance, fell down off the railing into the pit, and he was immediately attacked by 11 dogs,” Kraus said. “It was very horrific.”

It’s not yet clear whether the boy died from the fall or the attack, said Barbara Baker, president of the Pittsburgh Zoo & PPG Aquarium. Zoo officials at first estimated the boy fell 14 feet, but police said it was 11. It’s not clear which is correct.

The Allegheny County medical examiner planned an autopsy Monday, and the boy’s name was not expected to be released until that was complete.

Authorities said that zoo staff and then police responded “within minutes,” but visitors described that time as being filled with screams for help. 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.

Steve Feldman, a spokesman for the Association of Zoos and Aquariums, said no one he’s spoken to can recall any deaths of children at an accredited zoo over the last 40 years or more. Feldman said the Pittsburgh Zoo successfully completed its 5-year review in September, which means it meets or exceeds all safety standards.

Authorities didn’t release the name of the woman, 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 zoo was immediately closed, and it was not clear when it will reopen, authorities said.

The so-called painted dogs are about as big as medium-sized domestic dogs, and 37 to 80 pounds, according to the zoo. They have large, rounded ears and dark brown circles around their eyes and are considered endangered.

The attack happened in a 1.5 acre exhibit called the Painted Dog Bush Camp 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 roughly four-foot railing is located.

In May, some of the dogs crawled under a fence and escaped into a part of the exhibit that’s usually closed. The zoo was on lockdown for about an hour as a precaution.

Past fatal attacks at have prompted zoos around the nation to review safety features of their exhibits. In 2007 a tiger jumped over a wall at the San Francisco zoo, killing one visitor and wounding two others. Authorities first said the wall was 18 feet high, but a review found it was just 12  1/2 feet.

In September a man jumped off an elevated viewing train at the Bronx Zoo in New York and was severely mauled by tigers.

Kraus said there was nothing to prevent visitors to the painted dog exhibit from jumping into the exhibit area.

Police and the Allegheny County medical examiner’s office are investigating, and they haven’t yet interviewed the mother and father, who are receiving grief counseling.

Baker said the zoo, which has never had a visitor death, will also investigate. She said no decision has been made yet on the future of the exhibit.

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Associated Press writer Ron Todt in Philadelphia contributed to this report.