The 24-year-old singer and 21-year-old model got close Saturday in Domino Park in Brooklyn, according to TMZ.
Bieber and Baldwin were seen making out against a guard rail along the East River. The pair were spotted kissing again on a bench in Rockefeller Park in Lower Manhattan later in the evening.
Bieber and Baldwin are longtime friends who were first romantically linked in 2014. The pair sparked dating rumors again this month after they were spotted getting close in Miami.
"They have finally cleared the air and rekindled their friendship, and realized they genuinely have a lot of fun together," a source told E! News at the time.
"They both are single, and were very flirty with each other the entire night. They were inseparable the entire weekend," the insider added.
Bieber split from on-again, off-again girlfriend Selena Gomez in March. Baldwin was linked to Shawn Mendes after attending the Met Gala with the singer in May, but later told The London Times she's single.