A rescue chopper and several emergency crews were sent to the scene.
Paramedics and officers from Manning Great Lakes Police District performed CPR but he died at the scene.
Tuncurry Beach and Forster Main Beach are now closed.
The MidCoast Council posted to Facebook to confirm the closures.
"In response to a shark attack at Tuncurry Beach this morning, we have closed all beaches from Black Head to One Mile at Forster," the council said.
"This decision has been made based on advice from Surf Life Saving NSW officials. We will update here (Facebook) once beaches are reopened."
Police will work with the Department of Primary Industries to identify the species responsible.
One local posted on Facebook that there was an "eerie feeling" at the beach after what had happened.
"Rest in peace fellow waterman," the person wrote.
Tuncurry Beach is no stranger to visits from big sharks. In 2019, drone footage captured a great white shark swimming near the shallows where children were playing.
Police will address the media with more information later on Tuesday.