Beachgoers Witness 15-Ft Shark Kill Swimmer in Sydney

A beach in Sydney has been temporarily closed after some folks witnessed a gruesome killing -- a 15-ft shark devouring a swimmer.

A Rep for New South Wales Police Force tells TMZ ...  cops were called about the terrifying shark attack around 4:35 PM on Wednesday.

We're told folks were fishing off the nearby shoreline, and they heard the swimmer scream in terror and saw the entire attack unfold.

As you can see in the video, a shark was still lurking around and the guy recording yelled out, "Someone just got eaten by a shark. Oh man! Oh no! That's insane." He believes it was a great white.

Police say when they arrived, they could still see human remains in the water.

As of now, they don't know details about the deceased swimmer, but police said they are investigating and might know more info later today.