A hyena has mauled a 15-year-old boy at a camp in South Africa's Kruger National Park, sinking its teeth into the youth's face as he slept in a tent.

Erco Janse van Rensburg is in the intensive care unit of a Johannesburg hospital, where he has undergone reconstructive surgery, his grandfather said Tuesday.

"It's slow progress, but there's progress," Basie Smalberger said of his grandson's treatment. The teen, who was airlifted to the hospital after the attack at about 4:30 a.m. Sunday, is severely sedated and his medical team is waiting for facial swelling to subside, Smalberger said.

Janse van Rensburg had been camping with his parents and two sisters, his family said in a statement. The hyena dragged him about 100 feet before the boy's father chased it away, South African media reported.

Park rangers went to the Crocodile Bridge camp in Kruger, South Africa's biggest wildlife park, and searched in vain for the hyena, South Africa's national parks service said in a statement. They found a hole under the fence around the camp where the hyena may have entered, it said.

William Mabasa, chief spokesman for the parks service, did not comment on the details of Sunday's attack. But he urged visitors to wildlife areas not to feed animals because they eventually become habituated and gravitate toward tourist areas.

"Animals are naturally afraid of human beings," Mabasa said. "But once they start associating human beings with food, they lose that fear."