University student Cooper Hallam said he was 'hit hard' from the rear left side and then took two or three bites to his body before he could react and fight off the shark.
The attack took place at Kings Beach, in Caloundra, late on Saturday afternoon.
Photographs of Mr Hallam's wounds were uploaded to the Dorsal Shark Reports Facebook page along with a description of the attack.
'Shark was obviously small, couldn't fit jaws around my waist, but still enough to give me the fright of my life,' he wrote.
'Further inspection of the bite looks like the sharks jaw size is around the diameter of a dinner plate.'
'Still very rattled... Not freaking out quite as much as my Mum though.'
Photographs of the man's wounds were uploaded to the Dorsal Shark Reports Facebook
But Surf Life Saving Queensland Sunshine Coast duty officer David McLean told the Sunshine Coast Daily that local lifesavers had not received reports of a shark attack.
He said lifesavers were monitoring the water following the report of the attack.
'We would implore people not to be swimming around dusk or dawn when it is their feeding time,' Mr McLean said.
Further south in Ballina, a coastal suburb in northern NSW, there have been a spate of shark sightings and a number of attacks.
Last month 17-year-old surfer Cooper Allen was mauled by a 3.5 metre great white shark when he was surfing at Lighthouse Beach.
Up to 100 'smart' drumlines are set to be deployed along the northern NSW coastline in a desperate effort to keep swimmers safe from sharks.
Primary Industries Minister Niall Blair said 85 drumlines would be rolled out, with 15 already put in place.
The controversial shark management strategy helps authorities track and monitor sharks without baiting or killing them. The sharks are tagged and then relocated.
Comment: See also: Shark attack on surfer off Ballina, Australia; 6th attack for the area in 21 months