Expansion of the North Island rail network

In 1870 there were only 46 miles of railway in New Zealand, all of it in the South Island. Apart from a private coalmining line at Kawakawa in the Bay of Islands (which opened in 1867 and was horse-powered until 1870), the North Island was a land without railways.

By 1880 the North Island had 366 miles of railway, still way behind the 817 miles in the more populous and prosperous South Island.

Auckland's southern railway reached as far as Te Awamutu, while there were isolated sections in Taranaki, Hawke's Bay, Manawatū and Wairarapa. Between Waikato and Manawatū lay a vast upland of broken country, mountains, forests and Māori land.

Despite these difficulties, surveys of the possible routes were carried out in 1882–3 and in April 1885 the 'first sod' of the central section was ceremonially turned near the Pūniu River, south of Te Awamutu.

By 1890 workers had pushed the main trunk south from Te Awamutu to the Mōkau River and northeast from Marton (on the Foxton–New Plymouth line) to Hunterville.

In 1886 the Wellington & Manawatu Railway Company also completed an important line between Wellington and Longburn, south of Palmerston North, which would later form part of the main trunk.

The 1890s were a decade of frustration on the main trunk, when relatively little progress was made and the Liberal government came under fire for building 'political' branch lines at the expense of progressing more important lines such as the main trunk.

Elsewhere in the island, however, railways reached Thames and Rotorua, while a line through the Manawatū Gorge connected Palmerston North to the Hawke’s Bay and Wairarapa lines.

In 1900 a concerted effort was begun in the centre of the North Island and by 1905 the lines reached Taumarunui in the North and Taihape in the south.

Work began on the challenging Raurimu Spiral, by which the track would ascend to the Waimarino Plateau south of Taumarunui.

Further south, a series of massive viaducts were needed to bridge deep ravines at Makatote, Hāpuawhenua, Mangaweka and Makōhine.

By May 1908, after several years of intense effort, only a 15-mile gap remained between the unfinished Makatote viaduct and Ohakune. The Public Works Department rushed to complete a temporary, unballasted track in time for a 'Parliamentary Special' train to run to Auckland on 7–8 August.

With the official opening of the main trunk line in November 1908 (and the government's simultaneous purchase of the Wellington & Manawatu Company's line), the North Island finally had a mainline rail system to match the South Island.