The video footage appears to show two men being subjected to a foul-mouthed tirade by a British man and a woman, who spit on them and shout "F**k off back to Spain".
The 56-second clip also appears to show the Spaniards being punched by the woman as she clutches a portion of takeaway chips and chases them along the aisle of the topfloor of a double decker bus. At one point one of the Spaniards can be seen retaliating with a kick.
When the pair disappear down the stairs, a man with a Mancunian accent swears at them before leaning over and throwing a punch.
The incident happened last Thursday (12 February) at around 5am and was caught on camera by passenger Ross Thompson, 23, who uploaded the video to YouTube.
Mr Thompson told Mancunian Matters that other people on the bus were targeted. He said a man, unconnected to the first two men, was subjected to racial abuse by the group who believed that he was Spanish.
Thompson said he too had faced racial slurs from the gang, who thought he was Polish and told him to "f**k off back to Poland".
"This gang were out for violence," Thompson said. "The guy even had blood on his face before he got on the bus – it's just an average night out for them."
But the girl in the video came forward to defend herself, telling the Manchester Evening News that she had only been defending herself.
Louise Pare, 22, said she was the victim in the bust-up. "These Spanish lads were sat there and there was a chap with ginger hair there being all nice.
"One of the Spanish lads hit him and they started on him so I got involved to try and calm everything down.
"Then they turned on me and I just retaliated. The footage does not tell the whole story but I am not a racist. Some people were shouting but I did not shout anything racist," she said.