Searchers are hoping only to recover the body of a man missing since an attack by a number of sharks at a Perth beach, Western Australia's premier says.
Emergency services resumed looking for the 57-year-old at first light on Sunday after two teenagers on a boat saw what they believed was a shark attack at Port Beach in North Fremantle about 10am the previous day.
It's feared multiple sharks attacked the man, who is known as a regular swimmer at the beach.
WA Police Acting Inspector Troy Douglas said on Sunday morning officers were unable to confirm how many sharks were involved but it was "obviously at least one".
However, WA Premier Mark McGowan said later in the day it was apparent authorities were resigned to the fact the attack had been fatal.
"The events at Port Beach yesterday were horrific and very, very sad," he told reporters.
"A family is now grieving, a man has lost his life. It's a terribly sad situation."
Mr McGowan said he wanted to thank everyone on scene who had helped get swimmers and board riders out of the water, as well as the surf lifesaving volunteers who participated in the search that followed.
Everyone involved was doing what they could to recover the man's body, he added.
Insp Douglas said the teenagers on the boat had "made a fantastic effort" and "reacted really, really well" by alerting emergency services and providing information to assist the search.
All beaches in the area were closed and will remain so at least until Monday.
Fisheries Minister Don Punch said police had deployed a number of vessels to the area.
"I'd like to extend our heartfelt thoughts to the family of this man at this very difficult time," he said.
Warnings have been issued via the SharkSmart website and Surf Life Saving WA's Twitter feed.
© AAP 2021