A small circle of history researchers is racing to capture the last remnants of a little-known French dialect that endures in some old Missouri mining towns before the few remaining native speakers succumb to old age.

Missouri French is spoken by fewer than 30 people in Old Mines, south-west of St Louis, although dozens of others can still rattle off phrases from childhood songs or overheard conversations involving parents and grandparents.

Other languages once common in parts of North America have suffered similar fates, including some American Indian tongues, but Missouri French has the distinction of being one of only three dialects believed to have originated in the United States, and remained in wide use well into the 20th century.