'He’s dragging my son': 911 call reveals mother's fear when child fell into gorilla enclosure

This is the chilling 911 call from a frantic mother who watched her son being dragged by a gorilla in an enclosure at the Cincinnati Zoo.

Michelle Gregg 32, and her partner Deonne Dickerson, 37, have been at the centre of criticism surrounding the decision by zoo staff to fatally shoot ‘Harambe’ after their three-year-old son Isiah climbed over a barricade at Cincinnati Zoo in Ohio.

Authorities released the calls on Wednesday and in them Ms Gregg frantically tells the police dispatcher: "Hi, my son fell in the zoo exhibit at the gorilla - at Cincinnati Zoo."

"My son fell in with the gorilla. There is a male gorilla standing over him," she says. "I need somebody to contact the zoo please."

“Oh god, oh god, it’s got his pants, it’s taking the baby.

“He’s taking the baby into the cave. Oh my god.”

The operator asks the frantic mother how old her son is but at this moment she watches the gorilla drag her son around and ignores the operator and yells out to her son saying, "be calm".

"He’s dragging my son. I can’t watch this," the mother says before the line disconnects.

Harambe, the 17-year-old gorilla, was shot and killed by zoo staff on Saturday who have stood by their decision to shoot him, saying the 200kg animal could have easily killed the toddler.

Online petitions at change.org have more than 676,000 signatures demanding "Justice for Harambe".

The animal rights group Stop Animal Exploitation Now said it would file a negligence complaint against the zoo with the US Department of Agriculture.

The group is seeking the maximum penalty of $US10,000 (AUD$13,780).

The family have reportedly been receiving death threats after the endangered animal was killed and tens of thousands of people are demanding the mother to be investigated for child neglect.

A woman who filmed the video of the gorilla dragging the boy, Kimberley O’Connor, says she heard the child tell his mum he was going into the enclosure.

“I heard the exchange while I’m waiting. ‘I’m going to go in.’ ‘No, you’re not.’ ‘I’m going to go in.’ ‘No, you’re not.’ The mother turns around to her other children,” O’Connor told CBS.

Cincinnati police are investigating whether to bring charges against the child's parents.

Hamilton County Prosecutor Joseph Deters said in a statement that police would confer with his office after they had looked into the matter.

The family declined to comment on the investigation.

Genes of slain Cincinnati gorilla to live on

After the western lowland silverback was killed, zoo officials say they are collecting a sample of his sperm, raising hopes among distraught fans that he could sire offspring even in death.

But officials at the main US body that oversees breeding of zoo animals said it was highly unlikely that the Western lowland gorilla's contribution to the nation's "frozen zoo" of genetic material of rare and endangered species would be used to breed.

"Currently, it's not anything we would use for reproduction," Kristen Lukas, who heads the Association of Zoos and Aquariums' Gorilla Species Survival Plan, said.

"It will be banked and just stored for future use or for research studies."

That undercuts a weekend statement by Cincinnati Zoo Director Thane Maynard that the death of the silverback, who had been too young to breed, was "not the end of his gene pool".

Zoo officials did not respond to calls seeking more detail on their plans for Harambe's sperm.

There are currently 350 gorillas of Harambe's species in US zoos, according to the AZA, which accredits zoos, including Cincinnati's and approves breeding plans.

That population is large enough to maintain a breeding program so robust that many females of child-bearing age are given hormonal contraceptives.