While the StreetEasy analysis included all five boroughs, Manhattan had the most unsold condos by far: Over 2,400 of the unsold units, about 60 percent, were in the borough, primarily in large luxury buildings.

The Manhattan neighborhoods with the lowest share of new condo sales were the Lower East Side (32 percent sold), Midtown West, which includes Hudson Yards (55 percent), East Harlem (56 percent), Gramercy Park (60 percent) and Washington Heights (63 percent). The data represents a snapshot of what has actually sold since 2013, in buildings where closings have started to be publicly recorded.

The single largest reason the Lower East Side tops the list is because of the massive One Manhattan Square, an 815-unit skyscraper that towers over nearby Chinatown, where prices ranged from $1.2 million for a one-bedroom to over $13 million for a penthouse. Among seven new buildings in the neighborhood that have recorded sales, it represents three-fourths of the new inventory.

As of Aug. 26, the tower, which received a permit for occupancy in late 2018, had only sold about 20 percent of its units, Mr. Long said. A spokeswoman for Extell said there are “hundreds of more units” under contracts that have not yet closed.

That is a worrying sales pace for a luxury project with some of the most compelling incentives on the market. The tower was one of the last to receive a now-expired tax break that buyers will enjoy for several years. And the developer, Extell, the same company that built One57 and Central Park Tower, has engaged in some of the costliest promotions to lure buyers, including a waiver of up to 10 years of common charges on their most expensive units, potentially worth tens of millions of dollars to Extell. The developer began marketing in 2015, while the building was under construction.

Midtown West, which includes the sprawling Hudson Yards project, has several upcoming towers that have not yet recorded closings. But the recently completed 285-unit tower at 15 Hudson Yards was just 37.5 percent sold through late August, though marketing began in 2016. In January, the developer said that “over 60 percent” had sold, but that number includes units still in contract.

The slower rate of sales in Upper Manhattan neighborhoods like East Harlem suggests that developers may also have been too ambitious in pushing prices in less central, comparatively affordable markets, said Mr. Long.