The incident was caught on video, showing the bus branded as “Banyat Tohwong” parked on Damrong Rd at about 3pm.
Thick smoke was pouring from the engine bay where flames can be seen flickering through the engine bay cover.
A Phuket City Municipality fire truck arrived shortly after, with four firefighters quickly hosing down the flames.
The video was posted to the “Driving in Phuket like this must be reviled” Facebook page by user Suchart Nokkaew.
“The bus had about 10 Chinese tourists on board, but fortunately there were no injuries,” said Mr Suchart, who was at the scene.
“Luckily the Phuket Municipality fire brigade arrived in time to stop the fire,” he said.
Mr Suchart said it was not known how the fire had started.
Additional reporting by Shela Riva