The bus was carrying 43 school children, as well as the driver, from Strangford Integrated College to Bangor, when it crashed just after 16:00 BST.
Four of the pupils were treated in hospital with non-life threatening injuries.
“It just happened so quick,” Mr Smyth said.
“It’s just something you don’t want to see. Through the cracked glass, you could see the panic in their faces.
“They were crying and shouting for help, so we just attacked the glass like lunatics, and we got them out,” he said.
Mr Smyth said it was hard to believe that no one was killed.
“I definitely thought as we were breaking in that we were going to be lifting something out, some limbs or something, somebody.
“I just couldn’t believe there were just cuts and bruises, and yes, I’m sure there are a load of sore backs, because they were all threw about the bus,” he said.
He said the driver was “absolutely in shock”.
“There was a medic on the scene and he was more panicked about the driver because everyone was out, bar the wee fella who was trapped with his arm and the wee girl with her leg, she was trapped,” he said.
