Nicki Minaj derailed the “American Idol” auditions in Charlotte, North Carolina Tuesday, after swearing at Mariah Careyand threatening, “I’m gonna knock you out” … but Mariah FIRED RIGHT BACK with insults of her own.

It all went down while the two were sitting at the judge’s table … with Keith Urban sitting in between them and Randy Jackson sitting on the far end, next to Mariah.

We’re told the whole thing exploded over a disagreement over a contestant’s performance.

According to  MouthToEars.com, producers ended the auditions for the day so the two judges could cool down.  That’s been confirmed..

Big wigs on the show seem uncharacteristically upset by the blow up.  It seems producers are worried about Mariah and Nicki co-existing for the long haul. (y’think?!)