A serious brawl on a guided busway service heading to the borough led to police being alerted.
Blood splatters were left behind after a fight between passengers returning home from Christmas nights out in Manchester city centre in the early hours of Saturday.
The driver of the 11.40pm V1 bus alerted police after violence broke out on the East Lancs Road close to Albert's in Worsley.
Several passengers were left in tears after witnessing the extent of the fight on the lower deck.
One female passenger in her 60s said: "I've only come out for a Christmas night out and something like this happens.
"It will make me think twice about getting the late bus again. It was just horrible."
Two police vans attended the scene and officers questioned those who may have witnessed the confrontation.
But it is understood that those directly involved in the fight had left the bus before the officers arrived.
No arrests were made at the scene and the V1 bus was allowed to continue with its journey to Leigh.
Most of those aboard had been permitted to transfer to a following V2 bus, bound for Atherton, to avoid any further delay.
Another passenger, John Millar, 41, from Butts Bridge in Leigh, added: "There was not much warning really, though there were definitely some raised voices moments before.
"The bus pulled up outside Albert's and everything just exploded. But it was difficult to see much.
"There were women screaming and running upstairs, trying to get away from it, and blokes flying downstairs to try and intervene.
"Where it all happened, you could still see the blood on the floor, where they were scrapping."
Buses run between Manchester and Leigh until just before 1am on the guided busway.