I would say perhaps the Indus Valley Civilization, given that they had the assembly line, extensive commerce, the most advanced technology and by far the most advanced society of their day, but we do not know anything of them beyond their city ruins and artifacts other than a few scattered words transcribed in Sumerian Texts. However, this also makes such a possibility quite dubious, especially given the fact that they were still in the Bronze Age.
A very real possibility is Song China: In fact, it had most things we think of as being from Industrial Britain: The Bessemer Process for cheap steel, the corresponding puddling process for cheap wrought iron and a highly mechanized, water powered metal industry; water power was also used in mechanical clocks (like the famous one by Su Song), pound locks, irrigation, and wind power was also known; mass production of banknotes and metal tools in state-operated factories was routine; coal-based coke was used in smelting long before the West even knew of the it; movable type printing and paper were ubiquitous, even more so the cheaper block printing; literacy was far higher than any other major power elsewhere in the world; gunpowder, rockets and other firearms were invented; evolutionary theory and geology made great strides that would not be bested until Darwin's time; and even natural gas was used and pipelines of bamboo were known. IMO, it seems it was the Mongols that destroyed what really should have been the beginnings of a Chinese world.