Wairio Branch

Built at about the same time as the Riverton section of the Tuatapere Branch, what became the Wairio Branch left the Tuatapere Branch at Thornbury, where the junction originally faced Riverton rather than Invercargill, implying that the developers might have thought Riverton was going to be the region's major port. The line was built to open up new land to settlement and agricultural use and to access coal deposits. In 1879 it was opened to Otautau, and to Wairio on 3 March 1882, where it connected with private railways.

When the Tuatapere Branch closed in 1978 the Thornbury to Makarewa section became part of the Wairio Branch, and the closure of the Kingston Branch in 1982 meant that the continuation line to Invercargill section was also incorporated into the branch. This latter section of line is one of the oldest in New Zealand; built with wooden rails, it opened in 1864.

The development of private railway lines beyond Wairio was somewhat complex. The first was established not long after the Wairio Branch was opened and was a privately owned extension of a little over 2 miles (3.2 km) to the Nightcaps Coal Company in nearby Nightcaps, and operated by the Railways Department. The roads in the Ohai area in 1909 were described as "unspeakably bad" in a publication of the Ohai Railway Board in 1925; although significant coal deposits were in the area, it was difficult and hardly viable to transport the coal the short distance to the railway in Nightcaps. For this reason, another line from Wairio was proposed, but delays and negotiations meant that it did not open until June 1914. This line was operated by the Wairio Railway & Coal Company (WR&CC) and it served two additional mines in Moretown, a locality south of Ohai, but like the Nightcaps railway line, it did not provide reasonable access to Ohai's mines. Thus a third line was required.

While the WR&CC's line was under construction, mining interests in Ohai united to present a petition that the government acquire the WR&CC line and extend it into Ohai. Unfortunately, the arguments in favour of this proposal were presented to a parliamentary committee in 1914 just as World War I broke out and further consideration of the proposal was postponed. However, later that year the Local Railways Act was passed and, despite objections from the Nightcaps Coal Company and others in Nightcaps, the Ohai Railway District was declared on 4 May 1916. The declaration of this District included a condition that the Ohai Railway Board had to acquire the WR&CC line before constructing any new railway. The case for acquisition went to a compensation court, and, upon paying the sum of 19,862 pounds 6 shillings and 6 pence, the Ohai Railway Board took control of the WR&CC line on 22 June 1917.

The trackage acquired from the WR&CC was built to the low standards of a bush tramway, unsatisfactory as a permanent line. It could not even be appropriately extended into Ohai, though in 1919 an extension of 1 5/8 miles was opened to serve mines in the locality of Mossbank. In 1918 a proposal to build a third line directly from Wairio to Ohai was made, and it included a small deviation through Morley Village, considered part of Nightcaps. The construction of the line was opposed by the Nightcaps Coal Company, but after two commissions were held, approval was granted and construction commenced in July 1919. The first section was opened for traffic to Tinkers on 1 September 1920, but due to difficulties with the terrain it was not completed to Ohai until December 1924 and opened to traffic in the new year. In 1934 the line reached its ultimate terminus of Birchwood, 19 kilometres from Wairio. As the railway was built to national standards, the Ohai Railway Board suggested that the government could acquire it as the start of a route northwards to Lakes Te Anau and Manapouri, but nothing came of this.