"It's believed that when the attack occurred the man did actually see the shark and called out to try to warn others and very heroically his friends were able to bring him back into shore after he had been attacked," Superintendent Chris Schilt told reporters.
NCA NewsWire understands two tagged sharks – one measuring 2.5m and the other estimated to be up to 2.8m long – were detected on Monday night and on Tuesday, but neither was suspected of being responsible for the attack.
"Shark scientists have analysed photographs of the bite and determined a white shark of approximately 4.5m in length is likely responsible for the bite," the NSW Department of Primary Industries said in a statement.
SMART drumlines have been deployed at the beach following the fatality.
A rescue helicopter and several emergency crews were sent to the scene.
Paramedics and officers from Manning Great Lakes Police District performed CPR on the man, but he died at the beach.
"Bystanders, including a retired paramedic, did a valiant job pulling the patient from the water and commencing CPR before paramedics arrived," NSW Ambulance Inspector Joshua Smyth said.
"These people should be commended for their brave actions.
"Paramedics and police worked well together in what was a confronting scene in difficult terrain.
"Our sympathies are with the man's family at this difficult time."
Local lifesaver Brian Wilcox said the attack was "pretty unprecedented".
"I can't recall ever having a shark attack in this area," he told the ABC.
A drone had been circling the area and sharks had been spotted, he added.
Tuncurry Beach and other nearby beaches will remain closed for at least 24 hours.
One local posted on Facebook that there was an "eerie feeling" at the beach after what had happened.
"Rest in peace fellow waterman," they wrote.
Tuncurry Beach is no stranger to visits from big sharks.
In 2019, drone footage captured a white shark swimming near the shallows where children were playing.
Eight people were killed by sharks in Australian waters last year, according to the Taronga Conservation Society. A further 11 were injured.