We've spoken with multiple sources who have viewed surveillance footage recorded Sunday outside the APT 4B restaurant. We're told Chaka, his assistant and another friend were leaving an event, walking through the parking lot when Chaka was approached by another man.

Our sources say, in the video, Chaka and the other man start exchanging words, but things escalate, and the conversation becomes visually more intense ... all while the other man allegedly keeps his hand on and around his waistband.

We're told at one point, a female bystander pushed the other man away from Chaka, but he didn't back down ... and then things really got intense when Chaka approaches the man again, who seemingly bumps Chaka with his chest, and Chaka grabs the man by the collar.

From there, our sources say, a group of about 3 or 4 other men -- who'd been standing in the parking lot with the man confronting Chaka -- get involved, rushing in, and knocking Chaka to the ground with a punch followed by kicks and stomps.

We're told one guy in the group makes his way between 2 vehicles, produces a gun, and fires at least 2 shots. Our sources say Chaka, who was also armed, can then be seen getting back on his feet and firing at least one shot in return.

TMZ obtained the dramatic 911 call from the scene, where a man claiming to be restaurant security works to help Chaka ... who had suffered a gunshot wound in the exchange.

A source close to Chaka tells us he was shot at least once -- the bullet came close to his heart -- and he's currently in critical condition.

As for what started the verbal altercation ... we're told it's unclear, though it might have been some sort of dispute about the man not being allowed entry to a party.