'There was a lot of blood' - man recounts moment his friend was attacked by shark in Byron Bay, taking a chunk of his leg

A man remains in a critical condition and in an induced coma after a shark took a "chunk" out of his leg while he was surfing at Byron Bay in New South Wales..

Sam Edwardes 41, was surfing at Belongil Beach yesterday with friend Dane Davidson when he was attacked by a shark, Nine News reports.

"As soon as my mate got out the back, he sat up on his board and instantly a shark smashed from underneath," Mr Davidson said.

"It came up from underneath and knocked him clean off his board. There was a lot of thrashing and splashing. He started screaming.

"I didn't realise until I paddled with him back into the beach and there was a big chunk taken out of his leg. There was a lot of blood.

"A random bloke on the beach and I jumped in and wrapped ropes around his leg for a tourniquet because the bleeding was bad. Hopefully that prevented him from losing a lot of blood," Mr Davidson said.

Mr Edwardes was treated at the scene by paramedics, before being air-lifted to Gold Coast University Hospital.

The bite to his left thigh missed an artery by just millimetres. He has undergone more than four hours of surgery.

A New South Wales ambulance spokesman Daniel Willis said the actions of bystanders was "heroic".