NICKI MINAJ Goes After Mariah 'I'm Gonna Knock You Out'

Nicki Minaj derailed the "American Idol" auditions in Charlotte, North Carolina today, after swearing at her and threatening, "I'm gonna knock you out" ... sources tell TMZ.

Multiple sources are telling us there was a blow up between the two ... Nicki left, then came back and the fireworks continued, culminating with the threat.  We're told producers ended the auditions for the day so the two judges could cool down.

Big wigs on the show seem uncharacteristically upset by the blow up -- it appears this was no joke and it seems producers are worried about Mariah and Nicki co-existing for the long haul.