A spy told Page Six that Carter, 31, and Cyrus, 26, "made out against a wall like the entire night" in full view of other partygoers at a private NYFW bash at the ACME bar on Tuesday.
The paramours reportedly sipped cocktails and listened to music when they weren't playing tonsil hockey.
“[Miley] was all touchy-feely with Kaitlynn the whole night and kept making out,” the source said. “During the night, they stood up and started dancing with their friends in the section they were in and kept making out against the wall.”
Later, they celebrated more at La Esquina. A spy dished, “[It was] super PDA. They had their hands all over each others’ faces. There was lots of kissing and making out ... They were chillin’ and drinkin’ wine. Miley had that ‘wet hair look’ and they sat on the same side of the booth.”
Last month, Carter and Cyrus hooked up publicly in Italy just hours before the "Wrecking Ball" singer announced her separation from husband Liam Hemsworth — and just weeks after Carter and Brody Jenner ended their own relationship, which had been rumored to have been an open marriage. It was revealed after Carter and Jenner, 36, split that they were never legally married.
A source previously claimed that Cyrus' flagrant PDA with Carter put the final nail in the coffin for her and Hemsworth's eight-month marriage.
“He thought they could work it out, but all those pictures of her and Kaitlynn ended that,” the source added of the 29-year-old Aussie star. “Liam comes from a very conservative family and his family was freaked out by it.”
In another report about the couple released last month, a source told People that despite Cyrus' over-the-top antics – including "basically having sex" in public with rebound Carter – she "didn't want to hurt" Hemsworth.
Sources close to Cyrus previously accused Hemsworth of spawning the split with his alleged drinking and drug use, an allegation Cyrus herself hinted at in her song and video for "Slide Away." Hemsworth hasn't commented on the allegations.