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Two Australian adventurers who made history by kayaking unassisted to New Zealand set off on Monday hoping to bag a new record by walking from the Antarctic coast to the South Pole and back.

Justin Jones, 28, and James Castrission, 29, have each piled on 20 kilograms (44 pounds) and undergone months of intensive training for the 2,220-kilometre (1,360 miles) polar trek across some of the harshest terrain on Earth.

The pair will haul 160 kilograms (350 pounds) each of gear and supplies on sleds during their three-month journey, as they attempt to complete the world's first unsupported return journey from the Antarctic coast to the South Pole.

The adventurers are familiar with extremes, having battled giant seas, sickness, sharks and food shortages during their 62-day world record kayak crossing of the Tasman Sea in 2007-08, a 3,300-kilometre journey.

Jones said the cold would be their biggest challenge, something they had braced for at a training camp in the Arctic earlier this year.

"(It's) so cold that your breath freezes in front of your face, you get ice forming in your sleeping bag, it's intensely cold," he told reporters at Sydney Airport ahead of their departure for South America, where they will meet a Russian cargo flight bound for Antarctica.

Dried meat, nuts and powdered meals will be their fuel, and they aim to consume 6,000 calories a day, about triple the recommended daily average.

"That's 15 Big Macs of food worth a day, and we're still expected to lose a tonne of weight -- we're expecting 20-30 kilos each," Castrission said.

The psychological challenge would also be immense, he added, with their long-standing friendship likely to be tested at times.

"Spending three months out on the ice with your best mate, you're going to get the occasional tiff," he said. "But fortunately we've seen each other at our best and worst and we can work through it most of the time."

Castrission's mother, Vivienne, said the two men were well prepared and "they know what they are in for", adding that she was much calmer than before the Tasman kayaking trip.

"We didn't try to stop them this time, this is what they're going to do," she said.

Jones admitted it was "tough" on their families "but they're proud of us and they're supporting us." he said.

Aiming to raise money for a children's cancer charity, the expedition will officially begin at Antarctica's Union Glacier Camp on October 16.

The pair will document their journey with photographs, video blogs and via social media sites.