Pol Capt Thiwatpol Tawitsang, deputy inspector of Krathum Baen police station, said the fire started at the Toyoda Gosei Rubber (Thailand) factory in Tambon Omnoi at about 1.30am.
The parking lot is on the second floor of a stand-alone building so the factory itself was not affected.
The blaze was put out about 20 minutes after the fire engines arrived but the flames had already damaged 120 motorcycles parked there. Most were totally destroyed.
Workers told police that they saw a light sparking and that the sparks fell onto a motorcycle’s pillion seat causing it to catch fire. The flames spread very fast.
Police have yet to investigate and determine the cause of the blaze.