A surfer is in a critical condition after a shark bit off his leg at a beach in Western Australia.

Ben Gerring, 29, was in the water near Mandurah, south of Perth, when the attack occurred.

The attack occurred at around 16:00 local time (07:00 GMT) on Tuesday, theAustralian Broadcasting Corp. reported.

Local media reports said Mr Gerring was resuscitated before he was taken to hospital. He has undergone surgery and remains in a critical condition.

"He was right out the back looking to get a big wave, one of the set waves that had been coming through during the day," Brian Williams, president of the Mandurah Boardriders Club and friend of the victim, told ABC.

"He'd sort of paddled out the back, sort of past the pack slightly. And next thing all hell broke loose and they were trying to bring him in.

"His board was broken in half, they found the tail part of his board," Mr Williams said.

Surf Lifesaving Western Australia reportedly issued a warning before the attack, after an unknown species of shark was seen in the local area.