Three Thai workers died in an explosion at an ethanol plant in the north-eastern province of Khon Kaen in Thailand, police said on Monday.

Police Lieutenant Colonel Sarawut Dansuk said the three workers were repairing the lid of a wastewater tank at an ethanol plant. The factory belongs to Thai Ethanol Power Plc in the province of Khon Kaen, 390 km (240 miles) from Bangkok.

"It could be that there was some kind of gas that leaked out and caused sparks when they were welding the tank lid and that set off an explosion," he told Reuters.

"An autopsy showed they were killed by the impact from the explosion," he added.

The authorities are investigating if the ethanol company was responsible for the accident.