The National Park Service said the man, whose name hasn't been released, was bitten shortly after 11:30 a.m. about a mile north of the Avon Fishing Pier while he was swimming in a group. No other swimmers were injured.
The man received various injuries to his right leg and lower back, the Park Service said, and was airlifted to Norfolk General Hospital in Virginia.
An Apex man, Mike Will, posted photos to Twitter of the aftermath of the attack and told WGHP-TV in High Point that the victim was a 50-year-old man.
It is the fifth reported attack in the course of just three weeks along the North Carolina coast.
An 8-year-old boy was bitten earlier this week in Surf City, but his injuries were described as minor.
With the recent shark attacks on the minds of beach goers, business owners said their shops and motels have not been affected.
"Everybody is out in the ocean, having a good time and playing on the beach," said On Shore Surf Shop employee George Howard.
The last known encounter with a shark at the Cape Hatteras Seashore occurred in 2011 on Ocracoke Island, according to the Park Service.