Local residents reported the incident after some 20 riders on motocross bikes from out of town were seen at the cave, reported state news agency MCOT.
About 10 of the motorbikes were ridden into the cave, and raced an obstacle course around stalagmites.
The riders left about 20 minutes later, local residents said.
To protect ancient cave paintings at the site, the Fine Arts Department declared Toh Luang cave, Also known as Khao Pa Mak, a historic site on Sept 16, 2016.
A survey of the cave interior was conducted by Royal Forestry Department officials and local administrative organisation representatives yesterday (Mar 23).
Marks were found showing that the motorbikes had been ridden two levels in the three-level cave.
The officers found that some of the stalagmites and stalactites had been damaged, and tyre marks were found on ancient paintings on the cave wall.
A video showing the riders gathered at the cave, and then riding through the cave, was posted on social media, but later removed.
Officials are now trying to track down the riders and the organisers of the event, which they said may include local politicians.
Royal Forest Department Director-General Adisorn Nuchadamrong assured that the offenders would face charges for any damage caused to the cave.
Winit Relungla, a councillor with the Khlong Hin Tambon Administrative Organisation, said motocross riders were often in the area, riding through palm and rubber plantations.
However, the riders usually obtained permission first.
The riders might not have known the cave was off-limits, he said.
The cave had been used for filming for several major movies, including the Fast & Furious 9, Mr Winit said.