Other motorists alerted the driver of the six-wheel truck that something was wrong by honking horns and flashing their lights as he drove along the Buri Ram-Surin road.
Kamdaeng Phansaeng, 47, stopped the truck to check his cargo. He found flames and smoke coming from under the cavas covering his cargo of bicycles. Passing motorists stopped and search for water to douse the flames and others helped remove the canvas and called firefighters.
A fire truck later arrived to put out the fire Mr Kamdaeng told police.
He said he picked up more than 300 bicycles from a factory in Chachoengsao for delivery to shops in Nakhon Ratchasima, Buri Ram and Surin.
The fire damaged over 200 bicycles worth around 150,000 baht being delivered to the BigC Superstore in Surin.
Investigators suspect the fire was started by friction as the metal on the bikes rubbed together in the hot weather, and that the canvas was the tinder. Police were still investigating.
The sky was overcast in the region on Sunday afternoon, with the threat of rain.