Thalang police received an emergency call at 11:30pm but by the time they reached the scene the fire, in the left rear wheel arch of the bus, had been extinguished by local people and security guard from Siam Nissan, who had dragged a hose the 150 metres from the car showroom.
The bus was left with scorched paintwork at the wheel arch but was otherwise undamaged.
Sanit Kongmuang, the security guard, said that he had not seen the fire start but had been alerted by local people who had spotted it, and he had helped them to drag the hose to the fire.
Police discovered that the Bangkok-registered bus belonged to a company specialising in Chinese tourists. It had broken down a week before and had been left by the side of the road, unguarded.
They said they suspected the fire may have been started by a group of teenagers who had been seen in the area earlier on.
The owners of the bus have been contacted and told to remove it before it is damaged further by vandals.