NEW YORK (REUTERS) - A month after a record-setting swim from Cuba to Florida, Ms Diana Nyad has moved on from the real sharks of the Florida Straits to the metaphorical ones of New York City.

Ms Nyad, who last month covered the 110 miles (177 km) of open ocean in 53 hours on Tuesday set off on a 48-hour swim to nowhere in a pool in New York's Herald Square, in a charity event to raise money to help the 25,000 people who are still displaced from their homes a year after Superstorm Sandy hammered the New York and New Jersey coastlines.

The challenges are different in the 120-foot-long (37-metre) two-lane pool set up by sponsor Procter & Gamble for her attempt near a busy Manhattan intersection.

"In Cuba there was this huge emotional pressure," Ms Nyad told Reuters. "That was about setting a record. That was about ego.

This is about other people." Ms Nyad's swim will attempt to raise money for disaster-relief organisation AmeriCares by encouraging people to make online donations.

On Tuesday, members of the United States (US) Coast Guard, and New York's fire and police departments took turns swimming along with Ms Nyad, as her pink cap glided up and down the pool.

"It was unbelievable!" said firefighter Tom Dolan, 45, after emerging from his spell swimming with Ms Nyad.

Mr Dolan, who hails from the Breezy Point, New York, one of the shore towns hit hardest by the storm, said he is doubly appreciative of her effort "to help us keep our energy and focus and realise we are not done yet."

A roster of celebrities, including Olympic Gold medalist Ryan Lochte, was scheduled to join Ms Nyad in the pool, while others looked on. Joe Manganiello, of the HBO show True Blood said he came to celebrate Ms Nyad's achievement in the Florida Straits.

"What's unbelievable is that her first attempt was in her 20s," Manganiello said, referring to Ms Nyad's four failed attempts to conquer the distance before finally succeeding at age 64.

"What she shows is that if you don't fail, you don't come back harder."