It's the first confirmed fatal shark attack in Australian waters this year, though it's believed another man was killed by a shark off South Australia in January.
Paramedics were called to the beach, just north of Forster, about 11:20am on Tuesday, after the man in his 50s was bitten while surfing.
Police say the man suffered serious injuries to his upper thigh.
He was pulled from the water but died despite the efforts of bystanders and emergency workers to revive him.
Shark scientists from the NSW Department of Primary Industry have since analysed photos of the bite and determined a white shark about 4.5m long is likely responsible for the attack.
NSW Ambulance inspector Joshua Smyth praised the bystanders who entered the water to bring the injured man to shore despite the risk.
"Bystanders, including a retired paramedic, did a valiant job pulling the patient from the water and commencing CPR before paramedics arrived," he said.
Surf Lifesaving NSW has closed beaches from Blackhead beach to One Mile beach for at least 24 hours, and the DPI is deploying smart drumlines at Tuncurry beach.
Drones have been deployed in the area, as the DPI and police search for the shark responsible.
A great white shark was reportedly detected at nearby Main beach on Monday.
Local lifesaver Brian Wilcox said the attack was "pretty unprecedented".
"I can't recall ever having a shark attack in this area," he told ABC TV.
The DPI has advised water users and beach goers to follow the NSW SharkSmart Twitter feed or download the SharkSmart app for the latest information on shark movements and sightings.
Eight people were killed in shark attacks in Australian waters last year, according to the Taronga Conservation Society which records shark fatalities.
In January a Victorian man went missing in waters off Port MacDonnell in South Australia, and his torn wetsuit was later found, but his case was not recorded as an official shark fatality.
Source: Australian Associated Press
RIP
R.C.
P.s., Here, every surfer has scary shark stories - lots! I have several 'big shark' stories - there are two in particular that are really, really bad - just to type them up increases my blood pressure. (The one in Hatteras I wrote about was NOT one of them.) I write about this one (it was in South Daytona Beach) because of the conclusion I have only in recent years reached about it.
I'm going to keep it quick. It was strange but quick and I really wondered if my time was up. I was about 300 yards out and had allowed myself to drift north away from where most surfers were. There wasn't anyone within a quarter mile of me, probably more. I was just starting to get that uncomfortable feeling of 'this ain't the safest place to be' and my goal was to ride the next wave I caught into the beach.
As I sat on my board, staring out to sea, legs dangling like large bait, a MONSTER shark came from behind me and next to me. She was clearly checking me out - (I knew it was a she as she had mating scars on her dorsal fin which I could have reached out with my right hand and touched.) I remember thinking as I was in the process of going belly down on my board, 'if I grab her fin and jump on her back*, would that be considered a 'suicide?'
Anyway, there was always a problem with that which was for years I had thought it was a bull shark but research in these past few years shows that bull sharks never get that big. Now back when this happened we really thought that great whites were something Aussies and unlucky Jerseyites dealt with, but it turns out that there are quite a few here. My latest conclusion: I'm pretty certain that she was a great white - she was just too big to be any other type. There are many other facts of that event which likewise point to the conclusion. (E.g., dorsal fin shape, her left pectoral fin should have hit my right leg but she was so big that it probably swished under my right heel! etc.) So, 4.5M/15 feet great white sounds about the right size.
Scary times when you have to paddle in using only your fingertips.
R.C.
*This was long before someone ever said or memed that expression
RC