A shark has bitten a 68-year-old man several times off North Carolina, the seventh attack in the US state's coastal waters in less than three weeks.

The man suffered wounds to his ribcage, lower leg, hip and hands as he tried to fight off the animal at a beach on Ocracoke Island, said Justin Gibbs, a local emergency official.

"The individual was actually located right in front of the lifeguard tower when it occurred," said Mr Gibbs, who added that witnesses reported the animal was about 7ft long. "He was pulled under by the shark. He was bitten several times."

The victim was swimming in waist-deep water with his adult son about 30ft offshore, the National Park Service said. There were no other swimmers injured.

Seven attacks along the North Carolina coast in the space of three weeks makes it the most in at least 15 years. Most were attacked in similarly shallow water.

Experts say the recent spate of attacks along the coast of the Carolinas is due to so many more people getting in the water.

Holidaymaker Laura Irish Hefty said her husband saw blood on both the man's legs. The man was treated on the beach for about 20 minutes, according to Ms Hefty, and then an emergency helicopter flew him to a local hospital.

Swimmers were back in the water at that spot within a couple of hours of the attack, she added. "Nobody seems to be that scared," she said.