A surfer left in a critical condition after being bitten by a shark at Fishery Bay in South Australia is to be airlifted to Adelaide.

Police said the man was surfing about 350 metres offshore from Port Lincoln National Park when the shark attacked him shortly before 10:00am.

The man was taken to the Port Lincoln Hospital with life-threatening injuries.

The Ambulance Service said he needed to be resuscitated.

A MedSTAR chopper has landed at Port Lincoln Centenary Oval to airlift the man to Adelaide.

Police in conjunction with Fisheries SA, local council and Surf Life Saving SA are in the process of erecting signs on the beach warning members of the public of the shark attack.

A Port Lincoln man survived a shark attack at the same beach 10 years ago, according to media reports at the time.

The man was also surfing at the beach when he was attacked by a four-metre shark on Father’s Day.

He was able to fight off the shark.

Fishery Bay is a popular fishing and surfing spot in SA’s West Coast region.

ABC/AAP