Mr Turner said: “I was fine, the lady in front of me might have been concussed. The bridge itself wasn’t high enough to hit anyone’s heads but parts of the bus exterior have swung down.
“The man in the front seat was in a really, really bad state. He’s got a lot of blood and a massive gash on his head.”
First Bus said it was aware of numerous injuries and that one person had been taken to hospital.
A spokesperson said: “We have launched an immediate investigation and are also assisting Police Scotland with their inquiries.”
ScotRail has closed a number of lines due to the crash.
A spokesperson said train services between Glasgow Central and Ardrossan Harbour, Ayr, Largs, Gourock, Wemyss Bay and Paisley Canal will be cancelled, delayed or revised.
