The teenager, whose name was not reported, was surfing in Pohoiki Bay Sunday afternoon when the attack happened, KHON-TV, Honolulu, reported.
Witnesses said the shark bit the teen's leg.
"He was coming down the wave and a shark came from the side and took him out by the leg and that's all I could see right from there," said Issac Belisaro, who was surfing nearby. "I was so close to a shark attack, it was a life deal right there. I can't explain it. It was too much."
The teen was airlifted to Hilo Medical Center where he was joined by his family.
"Condition is good. Mean, big lacerations to the back of his leg," the victim's uncle said.
The local fire department was scanning the waters Monday morning for signs of the shark.