The Northern Territory's rescue helicopter has been called to help a man stung by the world's most venomous animal for the first time this season.

Key points: 23-year-old man stung in shallow water, 190km south-west of Darwin

23-year-old man stung in shallow water, 190km south-west of Darwin Sting believed to be first this season

Sting believed to be first this season Scientist predicts NT wet season may see increase in jellyfish numbers

The 23-year-old had been fishing with a group of friends from a small dinghy about 11:00am Saturday, when he stepped out to wade to shore and was stung by a box jellyfish.

He returned to the dinghy, which was near Channel Point, about 190 kilometres south-west of Darwin, and alerted his friends, who called emergency services before performing CPR.

The Top End Rescue Helicopter was sent to retrieve the man, CareFlight said, and he was transferred to the Royal Darwin Hospital in a stable condition about 12.30pm.

"This is the first box jellyfish sting we've been called out to this season," CareFlight media spokesman David Wheeldon said.

"CareFlight typically does deal with a number of these stings per year and they certainly can be life threatening.

"Unfortunately we expect [this sting] probably wouldn't be the only one."

The man was discharged from hospital later that afternoon.

The Royal Darwin Hospital has been contacted to confirm if it was the first box jellyfish sting it has treated this season.

The 23-year-old was stung in water near Channel Point. ( Supplied: CareFlight )

'Serious year' for jellyfish suspected

CSIRO jellyfish scientist Lisa-Ann Gershwin said she had a "gut feeling" the 2018/19 wet season may see an increase in jellyfish numbers, given low rates over previous years.

But she warned it was an educated guess, based on 25 years of research in the field, rather than a scientific certainty.

"I haven't actually heard details yet that give me any sort of clue as to how the season is going to be, in terms of the markers that we look for," Dr Gershwin said.

"Gut feeling … I think it might actually be a fairly serious year for jellyfish this year.

"The reason I say this is we've had a couple of mild years.

"And generally we see a fairly cyclical nature … so the fact we've had a couple of mild years makes me think 'Oh, I bet we're due'."

Dr Gershwin said it was the exact time of year scientists started to see more jellyfish, and they would be looking for a range of markers to help them predict how the jellyfish season would shape up.

They include weather trends, temperature trends, rainfall and the appearance of jellyfish at other locations.

The NT tends to report more stings from box jellyfish than Irukandji, a scientist says, ( Supplied: Surf Life Saving NT )

CPR critical following box jellyfish sting

The Northern Territory tends to observe more stings from box jellyfish, while the east and west coasts see more from Irukandji, Dr Gershwin said.

While "drop for drop" the venom from Irukandji is more toxic, she said they usually administered less, so first responders needed to work faster following a box jellyfish sting.

"The box jelly is the world's most venomous animal in terms of the typical time to death in a box jellyfish sting is about four minutes," she said.

"Many people die in two [minutes].

"If you're still alive after 10 minutes, you're going to stay alive, most probably."

According to Dr Gershwin, if someone is stung by a box jellyfish, first responders should administer CPR, before neutralising the sting with vinegar.

In the case of Irukandji, she said there was more time to react, but it was also more difficult to determine the cause.

"You get the sting and five to 40 minutes later, the person becomes quite unwell, but you might not realise it up front," she said.

Another key difference between the two "alarmingly toxic" stingers is that box jellyfish tend to be found in fairly coastal, shallow waters, while Irukandji are more often observed in open water, and around reefs and islands.

Dr Gershwin said the best way for people to protect themselves was to cover their skin while in the water.

"We don't have to get stung or stay out of the water. We can enjoy the water sensibly," she said.

"Between the flags is absolutely the safest place on the beach to swim."