The parents of an American student mauled and badly injured by two chimpanzees in South Africa described his survival Friday as "truly a miracle".

Andrew Oberle, 26, who is in a critical condition in hospital, lost an ear, several fingers and toes and a testicle when he was attacked last Friday after entering a restricted enclosure at the Jane Goodall Institute Chimpanzee Eden in the northeast of the country.

"We would like all to know that Andrew is recovering from his ordeal, although he still remains in a critical, but stable condition," said Mary Flint and Andrew Oberle senior in a statement.

Two chimpanzees violently attacked Oberle because they thought he trespassed on their territory.

Chimp Eden director Eugene Cussons shot and injured one of the chimpanzees while trying to break up the attack.

"It is truly a miracle that he survived this brutal attack," said Oberle's parents, who flew to South Africa after the mauling.

The masters student in anthropology and primatology at the University of Texas at San Antonio, was doing research at the sanctuary for abused and orphaned chimps.

His family thanked people in South Africa, the US and elsewhere in the world "for your prayers and well wishes."

Chimp Eden gained fame through an Animal Planet TV series called "Escape to Chimp Eden".

The sanctuary currently keeps 33 chimps, which do not naturally occur in South Africa, in three large camps.