Orlando Bloom threw a punch at Justin Bieber

Orlando Bloom threw a punch at Justin Bieber early Wednesday morning in Ibiza ... and Justin fled the restaurant -- this according to 2 eyewitnesses.


The eyewitnesses tell TMZ ... Orlando was in Cipriani restaurant which was packed with celebs, including Paris Hilton, and Diddy. 

You don't see Orlando swing, but the eyewitnesses tell us that's exactly what happened.  We're told Justin ducked the punch.  That's where the video starts and you hear Justin scream, "What's up bitch?"

We're told when Bieber left the crowd applauded.