The fire broke out at about 7pm at an engine oil storage tank of the Toyota plant in Ban Pho district, about 100 km east of the capital.
Executives of the Toyota plant and Chachoengsao Governor Ruengsak Mahavinitchaimontri visited the site at about midnight and held a press briefing later.
Pairoj Hirunruangrong, senior president of Toyota Motor Asia Pacific Engineering and Manufacturing Co Ltd (TMAP-EM), said the fire destroyed the storage, pallets, engine oil and ten forklifts.
Sporadic explosions were heard during the blaze. A dozen fire trucks were sent to the assembly plant.
There were no reports of casualties, as most workers were off for the weekend.
The governor said the company will today contact pollution control agency to invite its officials to check if there was pollution spreading to nearby areas following the fires. However they said they expected no emission of pollution because there were no toxic substances kept in the storage facility, although there could be haze or smoke from the fire.
The fire was put out before midnight of the same day, entirely by water. No chemicals or foam were used. All the water used in the process would be recycled. Toyota has also worked with government units in Chachoengsao, to evaluate the impact of this incident on the nearby community.
"Toyota will take all responsibility for this," Pairoj said.
Police earlier suspected that a worker left the battery of an electric forklift truck charging too long, and that it overheated and caused the fire.