A 60-year-old woman diver has died after apparently being taken by a shark, the second such attack off western Australia in six days.
The woman, who was diving off Perth, suffered injuries "consistent with a shark attack", police said.
A boat crew that arrived to help said the shark was longer than their 5.5m (18ft) vessel.
A 29-year-old surfer died after being attacked by a shark south of Perth earlier this week.
Western Australia police inspector Danny Mulligan said the latest incident took place on Sunday morning at Mindarie between One and Three-Mile Reefs, off the city of Perth.
A 43-year-old man who was diving with the woman, who has not been named, told police he felt something go past him and when he surfaced he saw a "commotion in the water".
After the boat arrived, it stationed itself between the male diver and the shark and he was able to get back into his own boat. He then noticed the woman had "suffered severe and fatal injuries", Mr Mulligan said.
"The boat the three fishermen were on was 5.5m long and they said the shark was longer than their boat," he said.
Beaches in Mindarie were closed after the incident.
Surf Lifesaving Western Australia had tweeted about a shark seen about a kilometre offshore at Mindarie 20 minutes before the apparent attack.
On Thursday, a 4.2m (14ft) great white shark was captured near Mandurah, but it is not known if this shark was to blame for the attack on the surfer.
Surf Lifesaving Western Australia had also reportedly issued a warning before that attack, after an unidentified species of shark was seen in the area.
In 2014, the government in Western Australia introduced a controversial shark cull after a number of attacks off the state's coast.