A Florida angler suffered a severe shark bite on board his own boat but was saved from death when a "hero" sheriff's deputy raced to the scene and tied a tourniquet around the man's badly injured forearm just in time.

The unidentified victim, who is in his 40s, was fishing Friday on the Amelia River north of Jacksonville when he reeled in a shark that bit him on his boat, WJAX-TV reported.

The Nassau County Sheriff's Office Marine Unit was patrolling the waters nearby when it received a distress call and raced to the scene to discover the victim with a "severe shark bite to his forearm" and had "lost a lot of blood," said Sheriff Bill Leeper.

"He was bleeding pretty bad," the sheriff said. "The deputy got on the boat, assessed him real quick, put a tourniquet around his arm that stopped the bleeding."

The unidentified deputy then piloted the fishing boat to a boat ramp in Fernandina Beach, where emergency medical personnel were waiting, Leeper said.

The victim was airlifted by helicopter to a nearby hospital where he was admitted in critical condition but was expected to recover.

Leeper praised the deputy as a "real hero" who "took care of the situation."