Stranded on a rusty piece of sunken ship, these two teenage girls were forced to watch helplessly as two sharks circled them for 40 minutes off a New South Whales beach.

The 14-year-olds thought they were going to be fish food as they waited to be rescued at Byron Bay on Wednesday.

The girls, who regularly swim out to the sunken ship known as The Wreck, were horrified to see a shark, followed shortly after by a much larger predator, when they had clambered on to the structure.

"They were right there, we could see them so clearly and fully thought if we lost our balance we were going to be eaten alive by sharks," a shaken Caitlin Robinson told The Daily Telegraph yesterday.

Caitlin and her friend Jett Coates had swum out to the popular spot which is just 50m off Byron Bay's main beach and were about to jump back into the water when they noticed a shark.

"We go out there all the time to jump off," Caitlin, a Byron Bay High School student, said.

"We've heard there had been some shark sightings but we thought nothing of it seeing as we hadn't seen any.

"I couldn't believe my eyes when I saw the first shark."

A nearby surfer heard the girls cry out and attempted to save them but a shark started swimming towards him so he went back to shore to raise the alarm.

As the crying pair sat clinging to each other waiting to be rescued "the worst possible" thoughts entered their minds.

"We were crying and shaking, holding on to to each other so we wouldn't fall off and thinking about the worst possible scenarios," Caitlin said.

"It felt like we were stuck in the middle of nowhere because the tide was starting to rise and it was getting pretty windy. The waves were knocking against the wreck."

She said at one point the smaller shark jumped over part of the wreck, while the larger one - which was "bigger than a Malibu surfboard" - kept swimming beneath them.

"They just kept circling and I was thinking, 'Do sharks jump?'," Caitlin said.

After a gruelling 40 minutes on the wreck, lifeguard boats rescued the girls.

"We won't go back out there in a hurry but we will go back swimming just in shallow water," she said.

North Region Lifeguard Co-ordinator Steven Leahy said the girls had to wait for help because there are no lifeguard patrols until December 10.

While volunteer lifesavers man the beach on the weekends, there is no one during the week.

"The alarm was raised by police who then contacted volunteers to come and get boats to save them," he said.

He said there had been 32 shark sightings and one attack in the Byron Bay area in the past six weeks.

Everything from great whites, tiger sharks, makos, bronze whalers and bull sharks had been sighted.

"The water is still warm, there are lot of bait fish close to shore and whales migrating with their calves, which is attracting them," Mr Leahy said.

Byron Bay woman Linda Whitehurst, 52, thought she was going to die when she was forced to fight off a great white shark at Byron Bay on October 15.