Several beachgoers helped the man to shore before more people joined in to wrap towels around the man's puncture wounds along his torso and leg.
Officials said someone had to rush to a nearby home to make the 911 call from a landline because cellphone service is so poor in the area.
“I went above my knees, my friend came in and dragged him, he was yelling, 'Get me out the water, shark, shark!'" said Thomas Buckett, of Smithfield, Rhode Island.
The victim was rushed to a helipad in Wellfleet, where the Medflight took him to Tufts Medical Center in Boston.
Witnesses said the man was in a panic, but remained conscious and was talking as he was taken by ambulance to the helipad.
“It seems to be getting worse, you hear about it every year but it’s crazy it happened while we were here," said Daniel Coco, of Buffalo, New York.
The harbormaster told WFXT that Long Nook Beach does not have lifeguards and only beaches with lifeguards are closed for shark sightings and attacks.
However, the town's website lists Long Nook Beach as closed to swimming until further notice due to the incident.
The incident reportedly happened "way offshore."
Following the attack, officials posted warnings and closed the beach to swimmers. However, despite the alerts, several people still ventured into the water before nighttime.
Witnesses told WFXT they saw a number of seals roaming the area right near the spot where the attack happened.
The last person to be injured by a shark on the Cape was also bitten in Truro in July 2012.
The Atlantic White Shark Conservancy issued a statement regarding today's attack:
“We offer wishes for a full recovery to the victim of today’s shark bite and convey our sincere sympathy to him and his family. Encounters with white sharks in which people suffer injuries are as terrifying as they are rare. While we still don't know all of the details of this particular bite, sharks are not known to target people specifically and when they do bite people it’s usually a case of mistaken identity. Sharks ‘test the waters’ with their teeth, much like we use our hands. It’s how they determine if what they encounter is prey or something to avoid. Here at the Atlantic White Shark Conservancy, we are committed to making beaches safer by studying shark behavior and sharing what we learn with the public and town officials to help reduce the probability of these kinds of interactions."
Truro police are handling the investigation.