More than 50 people were escorted from the coach after it caught fire on the A617 near Newark-on-Trent, Nottinghamshire. They had visited Skegness, Lincolnshire, for the day on Saturday when the horror happened.
The vehicle was left “severely damaged as the result of the disposal of smoking materials,” according to the fire service.
But the passengers avoided serious injury and were treated at the scene, the emergency services confirmed.
Video taken of the fire and submitted to Lincolnshire Live shows thick black smoke billow into the sky. Flames can be seen ripping through the coach, which suffered significant damage.
Four fire crews from across Nottinghamshire dashed to the scene on Saturday evening.
A spokesman for Nottinghamshire Fire and Rescue Service said: “We received a call at 7.08pm on the A617, Averam.
“The fire was put out by 9.30pm by which point the whole vehicle was severely damaged. It started in the toilet as the result of the disposal of smoking materials.
“We helped get 54 people off the coach.”
East Midlands Ambulance Service (EMAS) said treatment was given to some of the passengers at the scene.
A spokesperson for EMAS added: “We received a call at 7.16pm on Saturday, August 14 to Averham, Newark.
“The caller reported a medical emergency. We sent four paramedics in four ambulance cars and two crewed ambulances. We treated patients at the scene.”
Police were also called to the scene.
Skills Group, which operated the coach, declined to comment as they said investigations were ongoing.