- Shark attack happened at popular Oahu surf spot
- Family says most of surfer's leg had to be amputated
- It is the fifth reported shark attack in Hawaii this year
(CNN)Witnesses in the water and on land helped save a shark attack victim in Hawaii.
The incident happened Friday along the rugged north shore of Oahu at a popular surf spot known as Leftovers Beach.
Witnesses told CNN affiliate KHON that a man was sitting on his surfboard waiting for a wave when a shark attacked him from underneath.
The affiliate identified the victim as Colin Cook, 25.
Cook apparently hit the shark several times before it let go of his leg.
"He swam on his own free will to another surfer who threw him onto his board and paddled him straight to shore," his cousin Chris Webster told the affiliate.
A kayaker also assisted in the rescue, according to Shayne Enright of the Honolulu Emergency Services Department.
When they reached the shore, others jumped in to help.
Quick thinking good Samaritans used the surfboard leash to create a tourniquet to help stop the bleeding, Enright said.
A surfboard was then used to carry Cook to a nearby highway, where emergency medical staff loaded him into an ambulance.
He was transported to a local hospital trauma center in critical condition. His family told KHON that most of his leg had to be amputated.
Officials say witnesses told them the shark was up to 12 feet in length, but they did not know what type of shark it was.
Ocean Safety lifeguards alerted swimmers to the attack and warned them to stay out of the water. They also posted "Shark Sighted" warning signs along the beaches in the area.
This is the fifth reported shark attack in Hawaii this year.