The NYPD’s former Manhattan police academy building is being transformed into a shelter for hundreds of migrants as the city struggles to house the growing number of asylum seekers entering the Big Apple, The Post has learned.

Officials with the Office of Emergency Management were spotted on Thursday night setting up rows upon rows of green cots inside the first-floor gym of the Gramercy Park facility in preparation for an influx of up to 500 migrants.

Four buses of migrants arrived at the ad hoc shelter at separate times early Friday morning.

One source said the living arrangements would be in place for at least a week.

The old academy is no longer used for training, but law enforcement sources told The Post that a select number of police bosses still use the indoor shooting range — raising security concerns among some members of the force.

“This will be a security nightmare,” a Manhattan cop said. “They will have to put cops at all the doorways, plus over a hundred cops are assigned there with lockers where they have their guns. None of these people have been vetted.”

The NYPD’s Force Investigation Division, the unit that probes all incidents in which a cop uses force on the job, still has an office inside the building on East 20th Street between 2nd and 3rd Avenues.

Neighboring the nine-story building is the 13th Precinct house.

A retired cop questioned the logistics of the temporary shelter, as the showers and bathrooms are located on different floors from where the migrants will be sleeping.

“What genius came up with this idea?” the former cop said. “Doesn’t anyone think these things out?”

It’s not yet known where the migrants staying at the new shelter came from.

On Wednesday, Texas Gov. Greg Abbott shipped two busloads with 91 migrants — including 38 children — to the city.

Just days earlier, Mayor Eric Adams said Abbott had planned to funnel an increased number of asylum seekers to the sanctuary city — a move the NYC Mayor’s Office of Immigrant Affairs called “shameful.”

“He is using children, migrants to make political points,” said the commissioner of the office, Manuel Castro.

More than 59,400 migrants have arrived in the Big Apple over the last year — with many handed off from governors of red border states.

In just a four-day stretch over last week, roughly 1,100 asylum seekers entered the city between Wednesday, April 26 and Sunday, April 30, the latest City Hall figures show.

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