Witnesses say 28-year-old man from Port Lincoln was attacked just after 7pm on Thursday while surfing south of Streaky Bay on the Eyre Peninsula

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Emergency crews are searching for the body of a man believed to be the victim of a fatal shark attack in South Australia.

A 28-year-old man from Port Lincoln was attacked by a shark just after 7pm on Thursday while surfing near Granites beach, south of Streaky Bay on the Eyre Peninsula, according to witnesses.