Melbourne, August 20 : American endurance athlete Diana Nyad has completed the first day of a 166-kilometer swim from Cuba to Florida, fighting fatigue and jellyfish stings in a bid to be the first to make the crossing without a shark cage.

The 62-year-old Los Angeles woman was said to be comfortable, confident and swimming steady at around 50 strokes per minute despite painful jellyfish encounters overnight which left her with stings on her lips, forehead, hands and neck, the 50-member crew accompanying her said in updates to fans via social media.

After the first day she was about a third of the way across the Florida Straits, News. com. au. reported.

"Today is more like swimming. I don't know what you would call last night... probably surviving," Nyad said, according to a blog run by her support crew.

She wore a new-and-improved bodysuit, which covers her from head to toe except for holes for the eyes, nose and mouth, but it did not prevent all stings.

Nyad used backstroke at night to keep her face out of the water and avoid being stung and returned to freestyle swimming after dawn, said the crew, which works from five yachts and includes divers with shark experience as well as jellyfish experts. (ANI)