A WOMAN desperately called out "Shark!" as she was being mauled to death in a frenzied attack by up to three of them - but onlookers thought she had been joking.

The sharks struck as the 21-year-old victim, Sarah Kate Whiley, from McDowall in Brisbane's northside, was swimming with friends at Amity Point, off North Stradbroke Island, about 5.30pm (AEST) yesterday.

Within seconds they had torn off both the woman's arms and savagely mauled her torso and legs.

Two fishermen were the first to react, dragging her out of the water onto the beach.

Frantic bystanders scrambled for towels to stem the bleeding before a helicopter rushed the stricken woman to Brisbane's Princess Alexandra Hospital where she died of shock and massive blood loss.

The horror of the pack attack has stunned the carefree holiday haven just east of Brisbane.

Beaches have been closed as police and fishermen search waters off the Moreton Bay island for the shark that attacked in waist deep water yesterday.

Inspector Peter Harding said yesterday all beaches within a twokilometre stretch both east and west of the fateful spot - known as Rainbow Channel - had been closed.

In the first detailed description of the tragedy, Insp Harding said the victim had been swimming with three friends from a church group when she was attacked.

"She went down under the water ... after about five or six seconds the deceased came out of the water and screamed 'Shark' and of course people at the time thought she was only joking ... until they saw the blood," he said.

Two nearby fishermen managed to get the stricken woman from the water and onto the beach.

But the injuries were so catastrophic that little could be done.

She was airlifted to Brisbane's Princess Alexandra Hospital, where she died 50 minutes after the attack.

Insp Harding said the extent of the woman's injuries indicated it was a pack of bull sharks, noted for their aggressive nature at this time of year.

"She was bleeding quite heavily - I'm of the opinion of what I've seen and what I've been told, there was more than one shark involved, there could have been up to three," he said.

He said beaches east and west of Amity Point would be closed "for a while" as a precautionary measure.

He said police divers and fishermen were trying to hunt down the sharks to "retrieve what we can".

"If we found them I suppose we would try to retrieve them and see if they have any body parts," Insp Harding said. "Realistically it's virtually impossible."

Insp Harding said some locals won't go near Rainbow Channel, which he described as one of the deepest in Moreton Bay, "at any time".

"After Friday night's storm - the water was very murky and dirty, in fact so much so one of the locals

wouldn't go in and dive," he said.

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