The man, aged in his 20s, was bitten on the leg at Farm Break, near Bunker Bay Road in Naturaliste, around 2.15pm on Friday.

A St John Ambulance spokeswoman told AAP he is a local and felt a bump.

Other surfers helped pull him out of the water and described the shark as being four to five metres long.

The man's bleeding was staunched before he was flown to Royal Perth Hospital by helicopter.

The spokeswoman said his injuries did not appear to be very serious.

Nine News vision showed the man's surfboard had been destroyed in the attack.

"He's just sitting on his board and the next thing you know we just heard someone go 'shark'. I turned around and I've just seen this white (shark) kind of breach," one of the man's rescuers told the broadcaster.

"It just obliterated his board."

The beach has been closed.

There have been five fatal shark attacks in Australian waters this year.

One of them was in WA in January, when experienced diver Gary Johnson, 57, was taken near Cull Island, close to West Beach in Esperance.

A fortnight ago, a 10-year-old boy suffered shock and cuts when a shark ripped him from a fishing boat about five kilometres from Strahan on Tasmania's west coast.

Australian Associated Press