MANHATTAN — An off-duty NYPD officer was arrested early Wednesday morning for trespassing in an NYU dorm, police said.

Anthony Villalon, 23, was "incoherent" when he was apprehended for trespassing in Greenberg Hall, a dorm for medical students at 545 First Ave., across the street from the university's Langone Medical Center, about 12:55 a.m., an NYPD spokesman said.

It wasn't clear why he was in the dorm and he wouldn't explain himself, police officials said.

It wasn't clear how he accessed the building or where he had visited while inside, police said.

He was expected to be charged with criminal trespass, officials said.

The 10-story dorm has 24-hour security and is a mix of three-person suites and studios, according to the university.