A man fought to save his girlfriend from a fatal bull shark attack only to be nearly mauled to death by the animal himself.

Swiss tourists Livia Mühlheim, 25, and Lukas Schindler, 26, were swimming at a beach north of Sydney, Australia, when tragedy unfolded.

Ms Mühlheim was filming herself swimming with dolphins when she was attacked by the 10ft shark at dawn on Thursday. Bitten multiple times, she lost an arm in the assault at Kylies Beach.

Schindler managed to swim Ms Mühlheim back to shore and called emergency services, but suffered severe bites himself. A passerby likely saved his life by applying a makeshift tourniquet to his injured leg, authorities said.

Livia Mühlheim was killed by a shark

Livia Mühlheim was killed by a shark (LinkedIn)

Superintendent Joshua Smyth of New South Wales Ambulance praised the passerby who used clothing to help Schindler with his injury.

“I just really need to have a shoutout to the bystander on the beach who put a makeshift tourniquet on the male’s leg which obviously potentially saved his life,” he said. Schindler remains in hospital in a stable condition.

According to Mühlheim’s LinkedIn, she was a former synchronised swimmer and worked at a Zurich based wealth and asset management firm Bellecapital. Schindler’s profile states he is a security supervisor for the World Economic Forum and is currently studying a Master of Arts at the University of St. Gallen.

A forensic assessment by shark scientists at the New South Wales Department of Primary Industries concluded that a large bull shark was likely involved in the attack.

A bull shark was likely involved in the attack (file photo)

A bull shark was likely involved in the attack (file photo) (Wikimedia Commons)

Bull sharks are among the world’s most dangerous shark species. They can tolerate both salt and fresh water and are known to enter estuaries and rivers.

Shark specialists also noted the rarity of a single shark biting more than one person.

“Individual shark attacks are rare. And shark attacks on two people by the same individual is not unheard of, but it’s very rare,” Gavin Naylor, director of the International Shark Attack File, told the Associated Press. He added that the behaviour could depend on prey availability, shark age or feeding conditions.