The 15-year-old was in a serious condition after the attack, officials said.
The boy was sleeping alone in a separate compartment of his family’s tent when the predator attacked him.
South African National Parks (SANParks) spokesman William Mabasa told AFP the attack occurred around 4.30am.
“He screamed and his parents woke up. Fortunately a nurse was there, as well as one of our guides.”
The boy was flown to Johannesburg for emergency plastic and reconstructive surgery.
The hyena, which escaped, is thought to have entered the campsite through a hole in the fence.