According to law enforcement sources, things got violent when club patrons heard private security hired to work inside the club were double charging people to get into the VIP area -- where stars like Usher, Diddy and Nelly were partying.

Cops say pushing and shoving broke out, and as the masses were being thrown outside, that's when a shot rang out. A security guard was treated for a shot in the arm, but has already been released from the hospital.

TMZ has obtained exclusive photos of Diddy's bodyguards rushing the mogul out of Club Dream after allegedly fired a round inside the club. Diddy didn't even have time to put his champagne down before his hired muscle ran him out the back door. - Watch Diddy Run!

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