Justin Bieber and Sean Kingston were just cruising the Miami Beach strip looking like such BALLERS ... they had to flag down a cop to protect them from adoring fans.
Law enforcement sources tell us Biebs was driving a drop-top Rolls-Royce this evening on Ocean Drive -- with Kingston riding shotgun -- when a group of fans noticed them and started to gather around the car.
We're told Justin and Sean got the attention of a plain-clothes officer who stood guard until the crowd left.
Sources tell us the sick Rolls actually belongs to Kingston, who -- for some reason -- is cool with his 17-year-old pal taking the wheel.
By the way, it all went down in front of a Friday's. Hope they got some potato skins ... those are awesome.
JUSTIN BIEBER & SEAN KINGSTON
CALL FOR BACK-UP
ON MIAMI BEACH
7/29/2011 6:15 PM PDT BY TMZ STAFF
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