A 22-year-old woman has suffered a severe injury to her leg after being bitten by a shark while tubing in Florida.

Jessica Vaughn was swimming to a boating tube in Fort Lauderdale when the shark tore into her leg.

Kyle Branston, a friend who was tubing next to her, said Ms Vaughn first thought she had been cut by glass.

He said panic then spread when the group realised a shark was in the water.

"She said something bit her or cut her, and I first thought she was joking," Mr Branston said.

Ms Vaughn has had reconstructive surgery on her leg. Pic: @Ftlaudfire

"My instinct is: I'm in the water, she's bit by a shark and she's bleeding everywhere. There's nowhere for me to go, I'm next to her, I could be next."

The shark's teeth had cut deep into Ms Vaughn's leg, shredding muscle and exposing bone in a half-moon shaped wound.

Nick Russo, who was also tubing, said Ms Vaughn was also hit in the head during the attack.

Friends are asking people to donate towards surgery costs. Pictures: CBS

He said: "When the shark bit her down low, I guess the fin came up and hit her in the head."

After the attack friends pulled her on to the boat and rushed her to a nearby dock where paramedics met her and took her to hospital.

She has had to undergo constructive surgery to her shin and calf.

Her friends say she is uninsured and is unable to cover her medical bills with her job as a waitress.

They have set up a fundraising website and are appealing for donations.