Beyond Rolleston, three routes south were considered: The third option was chosen and the line was built through an at times relatively barren part of the Canterbury Plains towards Rakaia.

By the time the line reached Selwyn in October 1867, 35 km from central Christchurch the provincial government was so short of finances that construction was temporarily halted.

In 1870, Julius Vogel announced his "Great Public Works Policy" and placed a high priority on the completion of a line between Christchurch and Dunedin.

Construction not only progressed south from the Christchurch end and north from Dunedin, but also from the intermediate ports of Timaru and Oamaru in both directions.

At the southern end, the Dunedin and Port Chalmers Railway opened on 1 January 1873, the first 1,067 mm (3 ft 6 in) gauge line in New Zealand.

[2] On 1 September 1875 the line opened to Balclutha; the major town of the lower Clutha River region and 84 kilometres from Dunedin.

The first 17 km to Woodlands opened on 11 February 1874, but the whole section to Gore was not completed until 30 August 1875 as a hill cutting at Edendale caved in several times.

Leaving Christchurch at 6 am the train arrived at Dunedin at 6.40 pm; there was a breakfast with the Governor and other official guests at Oamaru, passengers were left behind at intermediate stops, and the train was assisted by the Double-Fairlie "Josephine" between Oamaru and Seacliff (where the engine was left for fitters as Ben Verdon the "K" driver made "Josephine" do too much of the work).

During their heyday, these steam-hauled expresses were famous for the speeds they attained across the Canterbury Plains along a section of track near Rakaia nicknamed the "racetrack".

An extra evening South Island Main Trunk (SIMT) passenger service for businessmen, to compete with the Starliner private buses on the Christchurch to Dunedin route, started in March 1953 with first-class, steam-heated NZR 56-foot carriages attached to overnight express freights 138 and 151 between Monday to Thursday,[7] departing Christchurch at 8:25pm and stopping for passengers only at Timaru, Oamaru (1:26am) and Dunedin at 4:58 am,[8] where the carriage remained stopped and heated at the platform until 7:00am.

88 seater railcars replaced this service in September 1956 with a 6 hour schedule, departing at 5:30pm and arriving 11:30pm in both directions, daily until 28 April 1976.

The railcar service offered a more convenient and comfortable, second-class timetable than the South Island Limited with its early departures and late arrivals in Southland.

[12] From 1949 to 30 September 1979 trains 189 and 190 ran an overnight weekend express Christchurch-Dunedin departing at a late 10.30/10.50 pm on Friday-Sunday to arrive 6:30/6:58am on Saturday and Monday.

An evening railcar service operated in the middle of the 20th century and took 6 hours 10 minutes between Christchurch and Dunedin: it was cancelled in April 1976.

As this short-distance local traffic declined in the 1950s and 1960s and branch lines closed, long-distance freight increased, with through services between the major centres rising to prominence.

Today, to meet the demands of modern business and to compete with road transportation, operations continue to be enhanced, and much traffic comes in the form of bulk cargo from large customers.