"It was a pretty big go at him, the shark had.
"It just goes to show how vulnerable you are when you're surfing."
In a chilling witness account, a surfer who was in the water at the time can be heard saying he "saw the shark swim under him" in a video posted to Instagram.
Elsewhere a man said he was walking on the footpath at the beach when he saw a surfboard floating "and a body was next to it".
"I just presumed he might have got knocked out because he wasn't moving in the water," the man told 7 News.
Several people helped drag the victim, who the witness described as being in his 50s, onto the beach.
"We got him onto the sand. There was a lifeguard 4WD there already ... and they had a stretcher. We put him on the stretcher but he was pretty much gone by then.
"There wasn't any blood.
"From the groin to his knee, there was nothing there. It was just like hanging there but not much."
Gold Coast Mayor Tom Tate has declared beaches will be shut from the NSW border to Burleigh tomorrow, with lifeguards patrolling the waters on jet skis while a helicopter will monitor from the air.
It is believed to be the first shark attack at a netted Gold Coast beach since a 20-year-old surfer suffered non-fatal injuries at Nobbys Beach in 2012.
Greenmount Beach, near the New South Wales border, is netted, but does not cover surface to bottom.
It's about 20km from South Kingscliff in northern NSW, where a 60-year-old surfer died after being mauled by a three-metre white shark in June.
- NCA NewsWire
