An American research student was in a critical condition in a South African hospital on Friday after he was dragged by chimpanzees into an enclosure at a primate sanctuary and attacked.

The mauled body of the student, identified in local media as Andrew Oberle, was retrieved from the enclosure by paramedics under armed guard at the Jane Goodall Institute Chimp Eden near the eastern town of Nelspruit.

"When we found him, he was in a foetal position underneath a lapa (a roofed, open-walled structure) with massive injuries, lacerations, abrasions, partial amputation from his head to toe," said Lloyd Krause, spokesman for the ER24 emergency service.

"He lost an ear, he lost a number of fingers and toes, he's got very deep wounds, he's got total removal of skin and muscle off his one leg and his one arm, fractures all over the place."

The man was with a group of tourists when the attack took place on Thursday. The Beeld newspaper said he had been at the sanctuary for two weeks and was giving a lecture to the group.

"According to eyewitnesses, two chimpanzees grabbed the man by his feet and pulled him under the perimeter fence and into the enclosure," said Jeffrey Wicks, spokesman for emergency service Netcare 911.

"The man was dragged nearly a kilometer into the large enclosure while being attacked by the two animals."

He is now in intensive care after undergoing surgery at the Mediclinic Nelspruit hospital.

"He has multiple injuries and is in a critical condition. He is under close observation in the intensive care unit and the next 24 hours are crucial," hospital spokeswoman Liza Pillay told AFP.

The sanctuary, which has temporarily closed after the attack, did not name the man but said he was a graduate student at the University of Texas at San Antonio studying for his masters degree in anthropology and primatology.

"This is a terrible tragedy that should never happen," said David Oosthuizen, executive director of the Jane Goodall Institute-South Africa in a statement.

"All our thoughts and prayers are with this young man and his family."

Oosthuizen said chimpanzees were wild animals that were defensive of their territory, and that those at the sanctuary had to be treated with caution as they had been subjected to injuries and abuse from humans.

"The safety of our visitors and staff is paramount," he said.

"We have never had an incident like this, and we have closed the sanctuary to investigate how we can try to ensure it will not happen again."

Chimp Eden is a sanctuary for rescued chimpanzees, an animal that does not naturally occur in South Africa, and is a joint venture between the Jane Goodall Institute-South Africa and a private park.

It featured in an Animal Planet TV series called "Escape to Chimp Eden".