The singer was on location in NYC this weekend shooting 'Joker 2,' and yes ... she and the team revisited the famous outdoor Bronx staircase that Joaquin Phoenix danced upon in the first flick. Based on these photos and videos -- it would appears Gaga does the same.

She and director Todd Phillips were seen one day going through the scene, and eventually the cameras were rolling ... with LG in full costume and makeup, and showtunes to boot.

You can hear Gaga singing her heart out as bystanders recorded nearby. The film crew tried their best to cover her up and block folks out, but the cat was way out of the bag on this one ... you could probably hear her from a mile away based on how loud she was crooning.

Seems like the whole musical element for 'Joker 2' is in full swing ... and Gaga is bringing it with her natural talent. As for her costar, he made it on set eventually -- and they were shot together in their comic book signature clown gear. Pretty cool to see 'em fully realized.

Based on Gaga's shorter hair ... it would appear her character goes through quite the transformation. Remember, we saw her with a slightly different look a couple weeks ago.

And, of course, based on all the set photos and clips that have leaked so far (a lot) -- we kinda get the plot too at this point ... Joker escapes from Arkham Asylum, and Gaga's Harley falls in love with the dude ... presumably joining him in his criminal mischief once out.

It's a bummer that everything's getting spoiled well before the film will come out, which won't be for at least another year and change. But it's pretty fun to see it all in action.