ADELAIDE, Australia -- A surfer was in critical condition after a shark attacked him Saturday in southern Australia, police said.

The 26-year-old man suffered "serious leg injuries" when he was attacked 40 kilometres south of Port Lincoln in South Australia state, police said in a statement.

He was flown by helicopter in critical condition from a Port Lincoln hospital to the main hospital in the state capital, Adelaide, the statement said.

Adelaide's The Advertiser newspaper reported a witness's description of a 6-metre great white shark biting off the surfer's leg, which had an ankle strap attached to his surfboard.

"I was just watching the shark go out to the ocean with his board still attached," the unidentified witness told the newspaper. "The shark still had his leg and he was still swimming around with it."

The witness, a surfer, said he was about 50 metres from the shark at the time and could see its "massive" pectoral fin.

Sharks are common off Australia's beaches, but fatal attacks are rare. The country has averaged fewer than two deadly attacks per year in recent decades.