HAVANA - The mother of three and grandmother of two is seeking to become the first to  complete the historic feat without a shark cage.

The 49-year-old, who left the Cuban capital of Havana shortly after sunrise Friday, had covered 80 kilometers (50 miles) some 24 hours later, her support team reported on Facebook.

“Throughout the night, jelly fish stings were constant,” the team said, adding that Palfrey’s mouth was “very sore and painful.”

But “she is in good spirits, smiling and swimming strong yet sore,” her husband Chris was quoted as saying.

The 166-kilometer (103-mile) swim was expected to take between 40 and 50 hours. Palfrey’s US destination is Key West in Florida.

Slathered in a fresh layer of sunscreen, Palfrey welcomed the new day in extremely calm seas, her team said, noting she was traveling at 5.6 kilometers per hour (three knots) with a stroke count of 71/72 per minute.

“A little excited, a little nervous,” Palfrey said at Havana’s Hemingway International Yacht Club before diving into the sea early Friday.

Palfrey is seeking to accomplish the feat in a “call for friendly relations between the peoples of the United States and Cuba,” according to the Cuban foreign ministry.

Cuba’s national commissioner for swimming, Rodolfo Falcon, told AFP that if Palfrey succeeds, “it will be something out of this world.”

“Sea conditions are not similar to the pool, where she trained for many hours. At sea, the salt water weighs you down,” said Falcon, who won a silver medal at the 1996 Olympic Games.

Susie Maroney, a former Australian marathon swimmer, swam from Cuba to Florida in 1997 when she was just 22, but she used a shark cage.

Veteran US endurance swimmer Diana Nyad, 62, has tried, and failed, to complete the trek three times, twice without a shark cage.

Her latest attempt was in September, when she quit two thirds of the way into the crossing after suffering dangerous jellyfish stings. She plans to try again this summer.

Two yachts, a kayak and a boat are part of Palfrey’s support team, which includes her husband Chris. The vessels are carrying ultrasound equipment to ward off sharks.

Palfrey, who was born in Britain and moved to Australia at the age of 19, is  among the most accomplished open-water swimmers in the world and has completed swims in the Caribbean and Pacific without a shark cage.

Two years ago, she crossed the Strait of Gibraltar between Spain and Morocco  in three hours and three minutes, setting a new record for women.

Last year, Palfrey -- who began swimming at age nine -- swam from Little Cayman to Grand Cayman Island, again without a cage