Surfers at the Bunker Bay in Western Australia had the shock of their lives when a bronze whaler fin mingled with them and attack a bodyboarder on Sunday, instantly killing the victim described only by police as a 21-year-old man from Sydney.

Authorities have so far withheld the full identity of the young man pending the notification of his family but police officials have reported that the incident happened at about 50 metres off the shore.

Quoting surfers who came to the rescue of the victim, police said the horrifying attack sheared off the man's lower limbs and as of press time, authorities have only recovered his upper body while a continuing search was being conducted to recover the victim's missing body parts.

Also, a search is now being conducted for the shark to possibly pre-empt another attack, which according to ABC is the first in Australia since a man was mauled in a similar incident at South Australia on February this year.

Police said that surfers witnessed the attack and were the ones who came to the aid of the bodyboarder, who officials noted had only been living in the area for a couple of years and is believed to be vacationing with his girlfriend.

Witnesses interviewed by authorities said that as many as 30 surfers were on the waters during the attack and they were the ones who brought the man ashore but police said he was already dead by that time.

Residents in the area were in total disbelief as some informed authorities that sharks were known to venture around the area but not to the point of getting near humans and attacking them.

"We had some sharks spotted far out at sea a few months ago, but they never come this close to the shore," one local was quoted by The Australian Associated Press (AAP) as saying.

Authorities have decided to cordon off the area while an investigation is underway and efforts are ongoing to retrieve the victim's remaining body parts, which police said was likely taken away by the shark.