Sam Edwardes, 41, was surfing at Belongil Beach at Byron Bay when he was attacked just after 6.30am on Sunday.
NSW Ambulance paramedics treated him at the scene for lacerations to his upper leg, before he was flown to Gold Coast University Hospital, in a critical but stable condition.
The Suffolk Park man has undergone four-and-a-half hours of surgery and remains in a serious condition in intensive care.
Mr Edwardes’s family have travelled from Byron Bay and remain by his bedside in hospital.
Mr Edwardes’s housemate, Dane Davidson, said the pair had only just paddled out when the shark attacked.
“As soon as my mate got out the back he sat up on his board and instantly a shark smashed from underneath … knocking him clean off his board,” Mr Davidson said.
“There was a lot of splashing and smashing and he started screaming.”
Mr Davidson said he paddled with his friend back to the shore.
“We didn’t realise until we were on the beach that there was a big chunk taken out of his leg so there was a lot of blood,” he said.
“I was freaking. When I heard the screams he was making in the water and then I saw a chunk of his board floating off, that’s when I realised it was pretty bad.”
Mr Davidson and several bystanders made a tourniquet using leg ropes and tied it around the man’s leg.
“He was conscious but … his eyes were drifting around a bit, he seemed a bit dizzy,” he said.
“He was saying his breathing was labouring … overall I think he was alright, he was just in a bit of shock.”
He said his friend was “in good spirits” when ambulance officers took him to hospital and thanked everyone for their help.
Detective Inspector Matt Keogh praised those who helped to stabilise Mr Edwardes at the scene and said they remained “very calm” throughout the incident.
Probably without their swift actions we could be dealing with a whole different situation here.”
Belongil Beach and Main Beach will be closed for 24 hours.
A DPI spokesperson said scientists had been unable to provide an estimate of the shark’s size due from the damage to the surfboard, but they believed it was a juvenile White Shark.
The Shark Incident Response Team has been mobilised, but no sharks have been picked up on VR4G listening stations around the time of the incident and none have been spotted by helicopters since.
It is the second incident on the far-north coast this weekend, after a highly experienced surf lifesaver went missing yesterday while swimming at Ballina.
The 69-year-old man — a lifelong member of the local surf lifesaving club — failed to reappear after entering the water at Lighthouse Beach.
Emergency services were called to the beach shortly after 10:00am and crews are continuing to search for the man today.
