The Australian was trying to become the first person to swim across the Straits of Florida non-stop without a shark cage.

It is the fifth failure involving three women swimmers who have tried to make the marathon swim since 2011.

Her support team released a statement saying she had been taken on to one of her support vessels after 11 hours in the water.

Diana Nyad, an endurance athlete who failed three times to make the same crossing and has said she would like to take another shot this summer, tweeted her commiseration.

"It's a tough night for Chloe McCardel, a superior swimmer and an exemplary spirit," Nyad wrote.

McCardel, 28, from Melbourne, had hoped to complete the swim in about 60 hours.