'Lord of the Rings' actor threw a punch at Justin Bieber, who saved himself by ducking. It is not known what sparked the fight, reported TMZ.
Orlando Bloom, 37, was in Cipriani restaurant when the incident occurred, according to eye-witnesses.
Justin Bieber yelled at Bloom before fleeing the place.
The argument may have been over Bloom's ex-wife Miranda Kerr, 31 as Bieber, 20, soon posted then deleted a picture of the model in bikini.
There were reports that Bloom was upset after Bieber got close to Kerr during a 2012 Victoria's Secret fashion show in NYC.
Bloom was seen hanging out with Bieber's on-off girlfriend Selena Gomez in April this year.