Swank apartments are begging for buyers on Manhattan’s “Billionaires’ Row” — with more than 40% sitting unsold in towers that top out at 100 stories, The Post has learned.

Five years after the iconic One57 building became the city’s first “supertall” residential skyscraper, only 84 of its 132 pricey condos have been bought — leaving more than a third of them still on the market and none under contract, according to data compiled by leading appraiser and researcher Jonathan Miller.

Six other nearby buildings have as much as 80% of their units available, the figures show, with the total value of all the unsold inventory estimated by one analyst at between $5 billion and $7 billion.

Another building that’s set for completion next year — Central Park Tower, at 217-225 W. 57th St. — will put an additional 179 apartments on the market.

Gary Barnett’s Extell Development, which also built One57, got state permission to start selling a Central Park Tower in 2017, but no deals have closed — which would push the overall unsold percentage to nearly 65%.

Online listings show asking prices for available units that range from $2.1 million for a 14th-floor studio at 100 E. 53rd St. to nearly $64 million for a four-bedroom, duplex penthouse on the 76th floor of 53 W. 53rd St.

Top broker Dolly Lenz blamed the stalled sales on the sky-high prices, saying, “When people come here from other parts of the country and from around the world, the first thing they want to see is Billionaires’ Row,” she said.

“We toured them through the properties but many felt they were too pricey for the market — $7,000, $8,000 and $10,000 a square foot,” she added.

Lenz said the high prices were caused by a combination of factors, including the costs of property, construction, financing and high-end marketing — and savvy developers who have clauses in their contracts that keep lenders from forcing them to drop prices, thereby cutting into their profits.

Some brokers said they feared the surplus of expensive housing in the area — between 63rd and 53rd streets, and Eighth and Lexington avenues — was an ominous sign for the future.

“Empty buildings are never good for the city,” one broker said.

“This happened in 1988 to 1992, when there were a glut of condos that didn’t sell. They were smaller and less expensive, but it led to bad times.”

Another broker said the prospects for selling the vacant apartments were grim.

“They are priced out of the constellation of buyers out there now,” the broker said.

“It’s all a function of price. You can do the most spectacular marketing and offer the most incredible amenities, but it all comes down to price.”

The impact of the oversupply isn’t limited to the developers and the lenders who financed the struggling projects, but also everyone from maintenance and service workers to the neighborhood’s restaurants and stores.

“There’s a whole food chain that relies on people living in these buildings,” one broker said.

Neighborhood resident and therapist Laura Miller, 35, said that “to find out that people aren’t living in the condos is just, ugh.”

“I wish this was all affordable housing,” Miller said.

“This really upsets me. So many are struggling in the city.”

An Extell spokeswoman disputed some of Miller’s data, saying that One57 “is over 85 percent sold in units and over 90 percent sold in value.”

Aby Rosen and Michael Fuchs’ RFR Holding, which built 100 E. 53rd St., also said 10 apartments there were under contract, as opposed to the nine Miller counted.

Additional reporting by Elizabeth Rosner