An Australian marathon swimmer hopes to be the first person ever to swim from Cuba to the US without a shark cage.

As well as the sharks, 29-year-old Chloe McCardel will battle exposure, swift sea currents, stinging jellyfish and extreme fatigue as she attempts the record swim from Cuba to Florida this week.

The 103-mile journey is considered the 'holy grail' of marathon swimming, with numerous failed attempts having been made at the treacherous crossing.

McCardel is a veteran swimmer of the English Channel and other endurance swims and believes she has the strength and the determination for the dangerous crossing.

"At the moment it's the most high-profile marathon long-distance swim, and swimmers really want to come here and be the first," she said in Havana, Cuba.

"It's very important; it's like winning a gold medal."

American Diana Nyad and Australian Penny Palfrey have attempted the crossing 4 times between them since 2011, but each time threw in the towel part way due to injury, jellyfish stings or strong currents.

Fellow Australian Susie Maroney did it in 1997 but with a shark cage.

McCardel says the swim is "50% further than any person has swum between two points of land in the ocean".

A 32-person support team that includes weather experts and doctors will accompany McCardel on her ocean odyssey, which should last about 55-65 hours if she makes it all the way.

To set the record the swimmer must remain in the water at all times, not even touching the side of any support vessels.

Every half-hour or so she plans to pause to eat and down a half-litre of energy drink to stay hydrated.

Meanwhile, special equipment will include an electromagnetic field in the water around her that is designed to keep sharks at bay.

Swimming for cancer research

McCardel is also swimming to raise money to support cancer research, people who suffer from the disease and their families, and promoting the idea that an active, healthy life can help keep it at bay. She is dedicating the swim in part to her mother, a breast cancer survivor.

McCardel, who lives in Melbourne, has been swimming since childhood and also competed in triathlons. As well as crossing the physical gap between the two countries she says she hopes to help bring Cubans and Americans closer by symbolically bridging the political divide.

"I would very much love to encourage people to come here as tourists and to engage more with Cuba ... to promote travel and great relations with Cuba. From what I'm learning it's a very beautiful country, and I feel privileged to have been invited here" she added.

Most US travel to Cuba is barred under Washington's 51-year embargo against the island, although Americans are increasingly travelling on legal cultural exchanges and family visits.

The two nations have been at odds since shortly after the 1959 Cuban Revolution ushered in Fidel Castro's Communist-run government, leading to decades of mutual suspicion and bad relations between Washington and Havana.