Onlookers have described the horrifying moment they saw a surfer being mauled by a 'monster' Great White shark on South Australia's west coast.

The man has been identified by the Adelaide Advertiser as Chris Blowes.

The 26-year-old is currently fighting for his life in hospital.

Mr Blowes was surfing about 350 metres offshore near Right Point on the south-western side of Fishery Bay in Port Lincoln National Park, when he was attacked at 9.45am on Saturday.

Mr Blowes was out in the surf with about a dozen others when she 'massive' shark struck.

Shocked witnesses recall seeing what they believed was a six-metre great white shark swimming away with the surfer's leg and a surfboard in its jaw.

'The shark came in and bit his leg off and the guys helped him in and carried him up the cliff,' said Glenn Lugg, who has been surfing in the area for 25 years.

Mr Lugg was told to call an ambulance while his fellow surfers pulled Mr Blowes from the water, up the beach on a surfboard and into a car to take the 26-year-old to hospital.

The shocked witness said the experience was 'pretty traumatic', but that everyone involved did a great job.

A friend of Mr Blowes, Ty Swan, described the 26-year-old as a 'good bloke', and that he had been bitten in the middle of the thigh.

Mr Swan placed a sign at the popular tourist beach to let others know of the attack.

Another witness, who was surfing at the time, told Daily Mail Australia that 'there was blood everywhere'.

The injured man was initially taken to Port Lincoln Hospital with life-threatening injuries but been been airlifted to Adelaide for further treatment.

The man was airlifted to Adelaide for further treatment after he was bitten by a sharkRead

Shocked witnesses said after the attack, which took place at Fishery Bay, South Australia, the six-metre shark was seen swimming away with the surfer's leg in its mouth

Another man said those closest to the badly injured surfer acted quickly without any thought of danger to themselves.

'I was just watching the shark go out to the ocean with his board still attached,' another witness told the Sunday Mail.

'Obviously the shark still had his leg and he was still swimming around with it.'

The man said even though he was 50 metres from the shark, he could see its 'massive' pectoral fin - and he had no doubts it was a great white shark, the most feared creature in the sea.

However details of the type of shark and the man's injuries have not been released or confirmed.

 Fishery Bay is on South Australia's west coast, which is about seven hours from Adelaide

Witnesses have described the horrifying moment that saw the man being mauled by a Great White shark

After the shark victim had been brought ashore and carried up a slope to a parking area, he was loaded into a car.

The man, who remains in a critical condition, has been airlifted via a MedSTAR retrieval team to the Royal Adelaide Hospital for further treatment.

Police were working with Fisheries officials, the local council and Surf Life Saving SA to post signs on the beach warning others promptly after the shark attack.

The attacked happened during conditions that police and marine experts have previously said are dangerous.

The overcast conditions make it difficult for surfers to see sharks that might be in the area and it is believed that sharks often mistake humans for seals or dolphins.

The incident comes after surfer Jake Heron managed to fight off a four metre Great White at the same beach 10 years ago which attacked him just 10 metres from shore by punching and kicking it

He escaped with 20 stitches in his arm and 40 stitches in his thigh.