A surfer who had his leg bitten off by a shark on South Australia's west coast remains in a critical condition at the Royal Adelaide Hospital.

Chris Blowes, 26, was surfing at Fishery Bay, about 40 kilometres south of Port Lincoln when the attack occurred 350 metres offshore.

He was taken to the Port Lincoln Hospital before the MedSTAR helicopter transferred him to the Royal Adelaide Hospital.

The Ambulance Service said he needed to be resuscitated.

In a statement, Mr Blowes's family thanked supporters and well wishers.

"Currently our sole focus is on our unified, unconditional support and belief towards Christopher's big fight he has ahead, and we ask that our privacy in being able to provide that is respected at this time," the statement said.

"From the bottom of our hearts we wish to thank his inspirational mates who rescued him and got him to safety and all of the wonderful medical professionals both here in Adelaide and in Port Lincoln who have attended to Christopher."

Fishery Bay is a popular surfing and swimming spot for Port Lincoln people, said the Mayor of the District Council of Lower Eyre Peninsula, Julie Low.

Ms Low said it was a terrible incident that will be felt by the whole community.

"It's a beautiful place and it's such a shame this has happened," Ms Low said.

"Our sympathy goes out to the victim, and his family and friends."