The 35-second clip shows a female police officer rush into the McDonald’s moments before a loud ‘bang’ is heard coming from inside the diner.
Seconds later people are heard screaming and fleeing the scene,while fighting can be seen in the background.
Eyewitness Jake Rogers, 22, who filmed the incident on Friday night, claimed it sounded just like a gunshot.
“As soon as we heard that we all ran away – I was genuinely scared for my safety,” he said.
“I wanted to get away from there as soon as possible. Several people were injured by punches being thrown and others were trampled during the brawl which must have involved more than 30 people.
“After the ‘gunshot’ sound I saw two police vans round the corner and stop outside the branch.
“It was like something out of a Hollywood film.
“I didn’t know what was going on, but I was really scared.”
GMP later said there was no evidence that a firearm had gone off.
It comes after police officers were attacked with missiles when they attended Piccadilly Gardens at 5pm on Friday to disperse up to 100 youngsters who were fighting.