Hunt on for Great White Shark that killed American diver of Western Australia (VIDEO)

Avalon Beach near Sydney, Australia, is closed to the public after a shark attack on a surfer on March 1, 2009.

West Australian authorities are hunting a great white shark that killed a 32-year-old American man at Rottnest Island on Saturday — the 3rd fatal shark attack off WA in 6 weeks, and 4th in 14 months.

The man is understood to have been diving alone about 500 yards off Little Armstrong Bay around 1:30 p.m., Perth Now reports, quoting police.

Witnesses on a dive boat saw bubbles in the water, then the body appeared with "obvious traumatic fatal injuries." 

Two people on the boat described the shark as a 10-foot great white, The Associated Press reports, quoting Western Australia Police Sgt. Gerry Cassidy. 

Rottnest Island is a popular holiday spot 11 miles off the coast of the WA city of Fremantle.

The authorities are clearing beaches and warning swimmers to keep out of the water, as the shark is still be in the area.

Earlier this month, Perth man Bryn Martin disappeared while swimming at the popular Cottesloe Beach.

(Down Under reports: Australia: Perth swimmer feared taken by great white shark)

And last month, bodyboarder Kyle Burden, 21, was killed near Bunker Bay by a Great White. 

(Down Under reports: Shark rips bodyboarder in half off West Australia beach

In August last year, surfer Nicholas Edwards, 31, was killed by a shark at a popular surf break near Gracetown.

Since 1991, there have reportedly been 25 fatal attacks off the Australian coast, and 10 shark-related deaths in WA.

Perth Now, meantime, claims based on an analysis of shark attack statistics that Mondays and Saturdays are the most dangerous to swim at the beach in WA, with most fatal attacks occuring in September and November.