HAVANA - Veteran US athlete Diana Nyad pushed into the second day of a 166km swim from Cuba to Florida, fighting fatigue and jellyfish stings in her bid to be the first person to make the crossing without a shark cage.
After 24 hours in the water, the 62-year-old was about a third of the way across the Florida Straits and the 50-member crew accompanying her said she was "very comfortable and confident."
Nyad was swimming steadily at 50 strokes per minute despite painful jellyfish stings on her lips, forehead, hands and neck, the team said in updates to fans via social media.
"Today is more like swimming. I don't know what you would call last night ... probably surviving," Nyad said on a blog run by her support crew.
The athlete and author took to the water in Havana on Saturday and aims to make land at the Florida Keys on Tuesday after about 60 hours in the water.
She is on her fourth attempt to travel the distance between the two countries, which have been at odds for over five decades.
The last was in September, when jellyfish stings forced her to give up after about 40 hours.
By 3.20 pm (1920 GMT) on Sunday, Nyad's team said she had swum nearly 38 kilometres after 23 hours and 37 minutes in the water.
A video posted on YouTube showed her singing tunes from The Beatles as she sipped water.
"There's no stopping her now," the crew said.
Nyad's first attempt to make the crossing was in 1978, when she was 28 years old.
Shoulder pain, asthma and ocean swells forced her to cut short another attempt in August 2011.
This time, the long-distance swimmer has a specially designed bodysuit to protect her against jellyfish that she wears at night, when the creatures are most active.
The suit did not, however, prevent all stings, including by dangerous box jellyfish.
Nyad used backstroke at night to keep her face out of the water and avoid being stung, said the crew, which works from five yachts and includes divers with shark experience as well as jellyfish experts.
She returned to freestyle swimming after dawn.
The swimmer comes up to her Voyager escort boat, which she is not allowed to touch, around every 90 minutes to fuel up, sipping on a concoction of nutrients, electrolytes and calories through a Camelbak hydration pack.
Overnight she had pasta and hot chocolate, the crew said. At other times, she has a spoonful of peanut butter, pasta or a bite of bread.
Stressing the immensity of the challenge, her team tweeted: "This swim is five English Channels, with sharks and box jellies added."
At night, the accompanying boats and kayaks use only red lights because marine biologists say white lights could attract jellyfish.