The Seddonville Branch, later truncated as the Ngākawau Branch, is a branch line railway in the West Coast region of New Zealand's South Island. Construction began in 1874 and it reached its terminus at the Mokihinui Mine just beyond Seddonville in 1895. In 1981 it was closed past Ngākawau and effectively became an extension of the Stillwater–Westport Line, since formalised as the Stillwater–Ngākawau Line.

The South Island, also named Te Waipounamu in Māori, is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, and to the south and east by the Pacific Ocean. The South Island covers 150,437 square kilometres (58,084 sq mi), making it the world's 12th-largest island, constituting 56% of New Zealand's land area. At low altitude, it has an oceanic climate.