A special zoo response team has shot and killed a 17-year-old gorilla that grabbed and dragged a 3-year-old boy who fell into his exhibit moat, the Cincinnati Zoo's director said.
Authorities said the 3-year-old boy, who fell 3m to 3.7m, is expected to recover after being picked up out of the moat and dragged by the gorilla for about 10 minutes.
He was taken to Cincinnati Children's Hospital Medical Centre.
Director Thane Maynard said the zoo's dangerous animal response team that practises for such incidents decided the boy was in "a life-threatening situation" and that they needed to put down Harambe, the 180kg male gorilla.
Maynard said he hadn't talked with the boy's parents yet."They made a tough choice and they made the right choice because they saved that little boy's life," Maynard said. "It could have been very bad."
He said the gorilla didn't appear to be attacking the child, but he said it was "an extremely strong" animal in an agitated situation. He said tranquilising the gorilla wouldn't have knocked it out immediately, leaving the boy in danger.
Maynard said it was the first time that the team had killed a zoo animal in such an emergency situation, and he called it "a very sad day" at the zoo. The lowland gorilla is an endangered species.
Harambe came to Cincinnati in 2015 from the Gladys Porter Zoo in Brownsville, Texas.
Hospital officials, who haven't named the child, said they couldn't release any information on the child.
Maynard said the zoo's Gorilla World area would be open as usual today. He said the zoo believed the exhibit remains safe.
They are still investigating, but zoo officials believe the boy crawled through a railing barrier, then fell into the moat.