A shark killed one person and seriously injured another on Thursday at a beach in Australia's eastern state of New South Wales, rescuers and police said.
The attack took place in the early morning, and one of the victims, a woman, died at the scene.
The other suffered serious leg injuries and was airlifted from the remote beach in Crowdy Bay -- around 250 kilometres (155 miles) north of Sydney -- to a hospital in a stable condition.
"They were known to each other, and they were going for a swim, and the shark attacked," New South Wales Police Inspector Timothy Bayly told reporters.
State ambulance inspector Joshua Smyth credited a bystander with potentially saving the man's life by wrapping a makeshift tourniquet around his leg.
"The courage from some bystanders is amazing in this situation -- to put yourself out there is very heroic," he added.
Steven Pearce, Surf Life Saving NSW chief executive, described it as "a really, really terrible incident".
"This area is so remote, there's no lifeguarding services up there at all," Pearce told local radio 2GB.
The beach and surrounding areas have been closed, and authorities are working to determine what species of shark attacked the two swimmers.
There have been more than 1,280 shark incidents around Australia since 1791, of which over 250 resulted in death, according to a database of the predators' encounters with humans.
Oceangoers are most likely to be bitten by great whites, tiger and bull sharks, the data show.
In September, a great white mauled a surfer to death at a popular Sydney beach.
The man, who left a wife and young daughter, lost "a number of limbs" and his surfboard was broken in two, police said.
Australia's oceans are teeming with sharks, with great whites topping the list of species that might fatally chomp a human.
Undeterred, Australians flock to the sea in huge numbers -- with a 2024 survey showing nearly two-thirds of the population made a total of 650 million coastal visits in a single year.
How best to protect people from sharks is a touchy topic in Australia.
Authorities have adopted a multi-layered approach -- deploying drones, fixing acoustic trackers to sharks so they can be detected by listening buoys near popular beaches, alerting people in real time with a mobile app and stringing up old-fashioned nets.
Researchers say shark lives, too, need protecting.
Globally, about 37% of oceanic shark and ray species are now listed as either endangered or critically endangered by the International Union for Conservation of Nature, a database for threatened species.