The seven-metre shark was seen near Marino Rocks on Adelaide's coastline on Sunday
The shark was seen 100metres offshore at the Marino Rocks on Sunday afternoon, a Shark Alerts South Australia Facebook post says.
Nearby Nippers events were cancelled and swimmers evacuated from the water.
'It's the biggest I've ever seen as a crew member in the Westpac chopper. We put it down as 7m the photo really doesn't do it justice,' an unnamed crew member wrote.
It is possible for Great White Sharks to grow bigger than six-metres - the largest Great White ever verified, shark expert Andrew Fox told the Daily Mail on Monday.
A 7-metre shark is the same length as two-and-a-half cars
'Honestly, a five-metre shark is an absolute giant and it looks twice as big - you can only imagine what a six-metre shark does to people's perceptions.'
The person who observed the Great White near Adelaide is quite experienced, which has given the sighting some credibility, but you can only verify its actual length when it's measured, Mr Fox said.
Pictures of the shark caused a stir on social media and many debated the estimated size of the shark (pictured)
The pictures posted caused a stir on social media, with some swearing never to step foot in the ocean again, and others arguing the great white was unlikely to be that large and labelling the sighting a 'fisherman's tale'.
'I wanna swear in terror but this is a family page so I won't and I bite my tongue,' one kayaker wrote.
'Bugger that, they can have the water, I will stay on shore,' one frightened man posted.
'I think it's ridiculous that some people actually think that we have it all figured out...do you actually think that we know the max size for these sharks or just the max that we have recorded? These are marvels of nature and I'm sure there are larger than 7 out there as well. Ohhhhh silly people....nature always wins,' a woman wrote to the hundreds of people debating the shark's size.
'Don't really matter if it's 4-5-6 or 7 meters. It's a BIG shark! When your in the water with a White, what's a small one?' another man argued.
Shark Alerts South Australia said the crew used their six-metre jet boat to estimate the great white's size.
Mr Fox said that there have been more shark sightings along the Southern Australia coastline, which could be attributed to conservation efforts and the decline of people hunting sharks.
'With the expanding population were going to intercept them a lot more often,' he said.
They sharks accumulate where they feed and the seals and whales they eat aggregate in those insular areas, he said.
Although the shark population is expanding, there hasn't been a 'large increase in shark attacks,' Mr Fox said.
'That's surprising because you would expect that with a lot more sightings and interactions that there would be more attacks then there are.'
A six-metre tiger shark was killed last year while it was swimming near Lennox Head, on the northern New South Wales coast.
A fisherman named Matthew came forward and said that he caught and killed the shark after it ate a hammerhead shark he was trying to lure in.
A six-metre tiger shark (pictured) was killed last year while it was swimming near Lennox Head, NSW
The shark, which was estimated to be 50-years-old, was regarded to be the largest ever caught on camera and was featured on Discovery Channel show Jaws Strikes Back.
The female Great White had several scars that researchers identified her by, a hole in her right trunk and damage to her dorsal fin and tail.
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