NEW YORK Olympic gold medallist Mary Lou Retton has made "remarkable" progress, her daughter Shayla Schrepfer said on social media on Saturday, after a rare form of pneumonia left the American fighting for her life.

The 55-year-old gymnastics icon has been in intensive care for several days as she was unable to breathe on her own.

"Prayers have been felt and have been answered," Schrepfer wrote in an Instagram post. "Although she remains in the ICU, her path to recovery is steadily unfolding. Her fighting spirit is truly shining!

"Her breathing is becoming stronger, and her reliance on machines is diminishing."

Nicknamed "America's Sweetheart", Retton's gold medal-winning performance at the 1984 Olympic Games in Los Angeles captured the imagination of U.S. fans and her hospitalisation prompted an outpouring of support.

A fundraising page set up by the family exceeded $400,000 in donations as of Saturday afternoon.

"Though it's a lengthy journey, witnessing these improvements is incredibly heartening," wrote Schrepfer. "She's responding so well to treatments."

(Reporting by Amy Tennery in New York; Editing by Ken Ferris)