Green’s Dictionary of Slang

a general admonition to stop what one is doing, e.g. to move on, to break up a fight or a meeting, whether of several people or a couple.

1938		R. Chandler ‘The King in Yellow’ in Spanish Blood (1946) 72: Break it up, kid. You heard me, I’m expected.
1953		K. Tennant Joyful Condemned 306: Break it up, Terry [...] Time you got back to the Wing.
1960		Wodehouse Jeeves in the Offing 39: Break it up, Bertie, break it up!
1973		(con. 1930s) F. Huelin ‘Keep Moving’ 22: Jocka intervened before a brawl developed. ‘Break it up,’ he said sharply.
1985		(con. 1969–70) D. Bodey F.N.G. (1988) 118: ‘Hey, assholes, break it up!’ [...] Everybody backs away from the pad.
1993		M. Myers et al. Wayne’s World II [film script] Okay, break it up. Show’s over. Nothing here to see.