The man in his 50s suffered critical injuries to his upper thigh while surfing Tuesday morning, according to NSW Police.
Emergency services were called to Tuncurry Beach, Forster, around 300 kilometers (186 miles) north of Sydney, at about 11.20 a.m. local time (9.20 p.m. Monday ET), police said.
The man actually spotted the shark early and tried to warn his friends, police superintendent Christopher Schilt told reporters at the scene.
Bystanders and paramedics worked together to save the victim, said the NSW Ambulance in a tweet Tuesday.
Officers from the Manning Great Lakes Police District tried to resuscitate him but he died at the scene, the force added.
The shark in question is believed to be around 4.5 meters (nearly 15 feet) long, said the NSW Department of Primary Industries (DPI), a government agency responsible for fisheries and agriculture.
Alongside police, the DPI is monitoring the area with drones and about 20 kilometers (12.4 miles) of beach has been closed off to the public for at least 24 hours.