Veteran US endurance swimmer Diana Nyad quit her historic attempt to cross the shark-infested waters from Cuba to Florida on Sunday after medics warned she had suffered dangerous jellyfish stings.

The 62-year-old, who was seeking to become the first person to make the 103-mile (165-kilometer) swim across the Florida Straits without a shark cage, had spent more than 40 hours in the water and completed 67 miles before ending her bid at 11:00 am (1500 GMT).

And yet it wasn't the threat of the predators that ended -- or at least put on hold -- her lifelong dream that she first tried at age 28, and then again last month. It was two Portuguese men-of-war, jellyfish whose stings had released potentially harmful toxins into Nyad's body.

"The medical team said I should not go another two nights in the water and risk additional likely man-of-war stings which could have a long-term cumulative effect on my body," Nyad said from the water before climbing aboard an escort vessel, her support team wrote on her website diananyad.com.

"But for each of us, isn't life about determining your own finish line?" she was quoted as saying.

"This journey has always been about reaching your own other shore no matter what it is, and that dream continues."

Earlier on Sunday her team said Nyad had been weakened by a series of painful jellyfish stings after starting her journey on Friday night.

Nyad was struck in the face and eyes late Saturday by what her team said was a "presumed jellyfish," which left her face swollen and in pain.

She received treatment Saturday night and resumed her swimming, accompanied by three shark divers, her support team wrote early Sunday in a blog post.

Because she was not out of the water to rest, an independent observer from the International Swim Federation said the endurance athlete could continue her bid for a swim record.

The veteran swimmer had been given an anti-inflammatory drug along with oxygen and other medication during her swim, but in the end, after 130,098 strokes, the effects of the stings and threats of more man-of-war attacks forced her from the water.

"Good job Diana. You still achieved something only a handful ever could," wrote supporter Ruben Garay on Nyad's website.

"You've inspired thousands of people with this amazing achievement. Remember, it's the journey, not the destination!"

A post by one Lali M. said: "You are an inspiration, a champion and a world ambassador for tenacity, determination and drive. I am in awe of you."

Nyad, who had completed two-thirds of the journey before pulling out, was undertaking the record attempt with a range of equipment aimed at keeping her safe from sharks. Some curious creatures came in for a closer look.

On Saturday, barracudas and a shark were spotted near her but not too close for comfort, her entourage said on Twitter.

"Around 1pm -- and don't everybody get excited here -- an Oceanic white tipped shark was spotted near Diana in the midst of the three-boat flotilla," it said.

One of Nyad's safety divers approached the shark, and it eventually swam away, the team said.

After jellyfish stings slowed her down early on, Nyad seemed to gain strength on Saturday, reducing her rest times and increasing her stroke speed amid surprisingly calm conditions.

That afternoon, facing a second straight night in the water, she was served a homemade chicken soup concoction prepared by the captain of one of the escort vessels, and the soup seemed to lift her spirits, the team said.

Nyad failed on two previous bids, in 1978 and again last month, in her quest to swim across the treacherous Florida Straits from Havana to Key West, Florida.

Shoulder pain, asthma and ocean swells hobbled Nyad's August attempt.

Nyad set an open sea record by swimming from the Bahamas to the Florida Keys -- a journey that is the same distance as the Cuba-Florida swim, but a feat she described as much less dangerous.

The swimmer set a record for circling the island of Manhattan at age 50, clocking in at seven hours and 57 minutes.

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