The party is the brainchild of Irfan Haque, 31, who oversees the Deco-tinged olive-and-cream lounge, which otherwise offers lunch, light meals and an elaborate afternoon tea. A successful New Year’s party that Mr. Haque organized in the room fed demand for more regular dance events, he said, so he hired the D.J. and has been promoting the night largely through word-of-mouth ever since. The next one is scheduled for April 22.

Thus far, Mr. Haque has been able to thread the needle between providing an energetic good time and meeting the rarefied expectations of the Pierre’s traditional clientele, as well as satisfying the co-op board that controls the building and the Taj hotel chain that operates it. Nonetheless, the party has a surprisingly open feel. It imposes no velvet rope, dress code or cover charge. And while the bar offers top-shelf libations — Veuve Clicquot, Johnnie Walkers Black and Blue, Macallan 25 — the budget-minded can easily nurse an $8 beer or one of the $14 specialty cocktails all night long.

Rumor has found fans even among the hotel staff members, who seemed to get a little looser once the music got going, heads bobbing to the beat, lips syncing to the lyrics. Although the men remained in their regular, buttoned-down hotel garb, the women swapped their modest day suits for more revealing club wear: a swingy, sleeveless black dress for one, a slinky lavender minidress and strappy gold heels for another.

Image Below, Nora Walsh, the hotel’s public relations director, center, wearing a tie, took to the dance floor. Credit... Michael Appleton for The New York Times

Several partygoers said they were surprised to find such a vibrant scene at the Pierre and in the neighborhood, which is not exactly brimming with hipness.

“It has a very classy vibe, but if you want to dance, you can,” said Lauren Yonda, 24.

Others praised the relaxed atmosphere and friendly attitude.

“A lot of clubs are very intense, and this place, it’s just easy to meet people,” said Carlo Nieva, 40, a member of the sales team at Armani Fifth Avenue, who had brought along a co-worker, Brandon Tagupa, to celebrate Mr. Tagupa’s 25th birthday. “The music is good, and the crowd really makes it.”