The 648 bus, which is owned by church group Antioch, hit the 12ft 3ins bridge on Marine Drive at 6pm on Monday.
The activity vehicle had been positioned on the seafront throughout the day. Glass windows shattered onto the road and public pavements when the roof was crushed after more than half of the vehicle became jammed under the Holyhead to Chester rail line.
Two passengers and the driver were on the bus. An ambulance and the police attended the scene and the driver was treated for shock. No-one was injured.
The accident had a knock on effect with hundreds of passengers stranded for hours on Rhyl railway station as the railway line was closed by the accident while investigators examined the bridge.
Peter Levers, Leader of the Antioch Church, Abergele Road said the main priority was to get the bus back in working order. The vehicle provides a social environment for teenagers' at night in Colwyn Bay.
"I'm just so glad that no-one was hurt. It is really lucky because a full window flew in the air and smashed. The driver is still understandably in shock. The kid's are gutted. They come to the bus for a hot chocolate and a chat. The bus is funded by members of the community and we decided to attend Prom Day to show people what we do."
An inspector from Network Rail attended the scene to assess the extent of the damage and as a result trains were delayed for a number of hours.
A number of eyewitnesses were gathered in the streets. A spokesman for North Wales Police said the vehicle was cleared at around 7.53pm.
Alan Pritchard, who organised Prom Day said the bus had been a great success with the hundreds of visitors to the area.
"Prom Day was the best yet and people enjoyed the activities that took place on the 648 bus. Children and adults joined in craft making activities."