A drone has captured the moment a shark came within metres of two oblivious swimmers off Main Beach at Forster in New South Wales.

Bystanders rushed to alert the pair of the close encounter - with what is believed to be a 2.5m Great White Shark - but experts say encounters like this are more common than you might think.

"For every one shark that you see, there might be 10 or 100 sharks that see you," Rob Townsend from SeaLife Sydney told 7NEWS.

"You just don't realise because they're not mindless killers.

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"If you think about how many people are in the water on a daily basis - especially in summer in Australia - you've got to imagine that this kind of thing is happening all the time and we just don't realise."

Innate fear

A new study found nearly three-quarters of people are scared of sharks and a third of us won't go in the water because of that fear.

The top two reasons people gave in the survey for being scared of the animals were that they attack people and the size of their teeth.

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But experts say encounters - while rare - almost always end in sharks avoiding people.

Experts also believe that there is a higher risk of drowning than being attacked by a shark.

"The rates of mortality from a shark attack in Australia are very, very low," Macquarie University Associate Professor Adam Stow said.

"Drowning is a much more likely occurrence than a shark attack."

The shark was spotted at Main Beach at Forster in New South Wales. Credit: 7NEWS

The 'Jaws' effect

Associate Professor Stow said films such as Jaws had something to answer for in shaping the public perception of sharks.

"When you think of movies like Jaws, for example - well, they're quite terrifying, and I think in some respects that's given a fairly unrealistic view of the way that sharks operate in the natural environment," he said.

"When people think of a shark, they think of a White Shark usually, or something with big teeth.

"The vast majority of sharks are not like that at all - in fact, the vast majority of sharks are harmless".

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Typical behaviour

Rob Townsend said the shark's proximity to the swimmers in the Main Beach drone vision was not unusual.

"This is just a natural part of this animal's day," he said.

"It's just swimming in the surf zone and not really bothering the people around it at all.

"I think the reality is that most of the time these animals are just swimming about.

"We need to know that it's their habitat that we're entering - and if we're sensible about the way that we do that, then we're going to be safe."