Brittany Clark, 31, was killed by an alligator in a rare attack at a river in Florida's Little Big Econ forest

A woman was mauled to death by an alligator while swimming in a Florida river as her boyfriend desperately tried to free her.

Brittany Clark, 31, from Orlando, was attacked in the Econlockhatchee River at Little Big Econ State Forest, about 25 miles north-east of the city, on Sunday. Officials said the rare attack happened after the couple stopped to swim in about 3ft of water during a hike.

In harrowing 911 audio, Ms Clark's boyfriend is heard telling the operator: "Both her arms are dislocated - off basically," before adding: "One arm is completely off."

Screaming and crying can be heard in the recording as he pleads for help, saying he is "still trying to get her arms away from the alligator's mouth" and urging first responders to hurry because she is "losing a lot of blood".

A medical examiner's report has since revealed that Ms Clark's boyfriend, Chance, heroically fought the alligator as it dragged them both underwater in a spinning manoeuvre known as the "death roll".

"While they were swimming, an alligator grabbed [Ms Clark] by her arm and began the "death roll"," the report seen by the Daily Mail states. "Her boyfriend Chance grabbed the alligator, trying to get it to release her when it took them both underwater."

The report says Chance managed to free her arm "for a moment", but the alligator then clamped onto her other arm.

"Chance attempted to bring them both to shore when the alligator finally let go and CPR was started on shore by her boyfriend, and 911 was called," the report states.

Florida Fish and Wildlife Conservation Commission (FWC) spokesperson Chad Weber told reporters on Monday that the couple were hiking and had stopped to swim.

"It doesn’t seem they were doing anything malicious. They were in approximately 3ft of water," he said.

"She was bitten on both of her arms. The boyfriend was the one that made the phone call. He was trying to get her from the alligator’s mouth, and on the way to the hospital she did pass away from her injuries."

Authorities removed and euthanised two alligators - measuring 12ft and 13ft - from the river and sent them for DNA testing, Weber said.

We offer our condolences to this young lady’s family," he added, without disclosing the victim's identity.

The FWC reports an average of about eight unprovoked alligator bites each year. Since 1948, there have been just 26 fatal alligator attacks in Florida. The state is home to an estimated 1.3 million alligators.