Beachgoers are being warned not to approach a leopard seal which has set up camp on a beach at Iluka on the north coast of New South Wales.

Key points: The 3.5-metres marine animal is an apex predator with lethal teeth

The 3.5-metres marine animal is an apex predator with lethal teeth Signs have been posted on the beach to deter beachgoers from getting too close to the seal

Signs have been posted on the beach to deter beachgoers from getting too close to the seal A 23-year-old researcher was killed by a leopard seal while snorkelling in Antarctica in 2003

The animal is thought to be 3.5 metres long and has been making its way north along the coast for the past month.

Tony Belton has been photographing the leopard seal from a safe distance and said not everyone was being cautious of the marine mammal.

"I used my long telephoto lens, of course, so I could be a long way away," he said.

"I went down this morning, early, to check on it to find a couple with a young toddler with their iPads and mobiles standing not 2 or 3m away from it, with a kid running around, unrestrained.

"I could not believe it."

Leopard seals are apex predators with a ferocious array of lethal teeth.

Mr Belton said he shouted at the trio to move before explaining how dangerous the animal could be.

"It was a sleepy-looking thing but apparently they can spring into action really quickly," Mr Belton said.

"You never get between it and the water.

"Unfortunately these people were on the wrong side of this animal — between it and the water not 2m away."

The leopard seal has been tracking north for the last four weeks. ( Supplied: Tony Belton )

Warning signs posted

Mr Belton said NSW National Parks and Wildlife Service (NPWS) rangers had posted signs on Iluka beach warning beachgoers to keep their distance from the animal.

"The trouble is they [leopard seals] go and fish at night and [it] has come back in down the beach a bit further than the sign," he said.

President of the Organisation for the Rescue and Research of Cetaceans in Australia (ORRCA), Jacqueline O'Neill, said many people were not aware they could be fined for going near the animal, which could make a perceived photo opportunity a very expensive selfie.

"There's a legal 40-metre exclusion zone around the seal and people leave themselves open to prosecution if they get too close," she said.

"We have seen people get some pretty hefty fines in the past from getting too close or interfering with them."

The NPWS is warning beachgoers to keep their distance from the leopard seal. ( Supplied: Tony Belton )

In 2003, 23-year-old British researcher Kirsty Brown was fatally attacked by a leopard seal while snorkelling with colleagues in Antarctica.

Ms Brown was believed to be the first human fatality as a result of a leopard seal attack.

However, other people who came too close have been attacked.

'Beautiful animals but don't touch'

Alstonville environmental scientist Gordon Fraser was working as a Parks ranger on Phillip Island's Seal Rocks, in Victoria, when he was bitten by a leopard seal when trying to free a seal from fishing gear.

"The standard method was that one person would get in front of the animal to distract it and the other would go behind and lift the flippers up," he said.

"Then the person at the front would cut the obstruction off and say 'clear'."

On this occasion, Mr Fraser's colleague said "clear" and a split second later said "no, not clear" but the seal had already swung around and bitten Mr Fraser's hand.

"Its teeth went through my hand," he said.

"I had stitches inside and outside and got toxoplasmosis and my hand blew up like a basketball.

"They are beautiful animals but please don't touch them."

Leopard seals head north to feed

Leopard seals are commonly found in Antarctic waters, however the NSW far-north coast, long a magnet to tourists for its beautiful beaches, seems to be growing in popularity with the seldom-seen marine mammal.

Ms O'Neill said in the past five years the number of leopard seal sightings in subtropical waters had increased.

"We've probably had 5–10 leopard seals around the same area and there have actually been leopard seals sighted as far north as Queensland in the past," she said.

"They do come north in search of food [but] it is quite unusual.

"A lot of the time they'll be on remote beaches and you won't hear about it."

Leopard seals appear docile but can react quickly if they feel threatened. ( Supplied: Tony Belton )

Seal 'may need to be euthanased'

Marine veterinarian Duan March has been tracking the progress of this leopard seal since it was first seen at Crowdy Head about a month ago.

About a week ago it moved north to Port Macquarie, then Lake Cathie, Sawtell, Red Rock and now Iluka.

Dr March said the leopard seal was not in good condition and may need to be euthanised.

"It is covering a lot of distance and it does have declining body condition," he said.

"If its body condition continues to deteriorate it may need to be euthanased, but then, if it arcs up when we approach it, perhaps it's strong enough to keep going."

Last year Dr March attended a leopard seal with a stingray barb in its face at Yamba. That seal was seen safely off to sea.

But it was not a happy ending for another leopard seal found last year at Minnie Water with a chunk of flesh missing from its shoulder.

The injured leopard seal in northern NSW in 2018 was euthanised. ( Supplied: Aidan Ricketts )

That animal was thought to have been bitten by a juvenile great white shark.

It initially returned to the sea but then came ashore in an emaciated condition shortly after and was euthanised.

An autopsy revealed the animal had nothing but sand in its stomach.