Media playback is unsupported on your device Media caption Eyewitness: ''A massive white shark was circling the body''

A man has been killed by a shark off the coast of Western Australia, in the latest of an unprecedented series of such attacks.

The man was surfing with friends early on Saturday morning near Wedge Island, about 160km (100 miles) north of Perth.

The authorities say they are trying to catch the shark involved.

It is the fifth fatal attack off Western Australia since September. On average, there is one a year in the whole of Australia.

A witness, who was jet-skiing nearby, said only half a torso was left of the victim, and that he was himself attacked when he tried to help.

"There was just blood everywhere and a massive, massive white shark circling the body," he said, estimating that the fish was four or five metres (13ft-16ft) long.

"I reached to grab the body and the shark came at me on the jet-ski and tried to knock me off. I did another loop and when I came back to the body the shark took it."

The victim's remains have not been found, and a search is under way for them, police said.

The spate of fatal attacks in Western Australia has prompted calls for a cull of sharks, but the authorities have ruled out the option following protests from environmental groups.

Tony Cappelluti, of Australia's department of fisheries, told ABC television that the shark would be killed if tracked down.

"We have placed baited lines in the water near the attack site, in an attempt to catch the shark should it return to the location or pose a threat in the area," he told the Western Australia newspaper.

Sharks are a common feature in Australian waters but attacks are rare, with only 46 fatalities in the past half-century, according to the Australian Shark Attack File.