North Auckland Line

The North Auckland Line is a major railway line in New Zealand's national rail network. It runs from a junction with the North Island Main Trunk Railway in Westfield to Otiria via Newmarket and Whangarei. The first section was opened in 1868 and the line was completed in 1925. The line is currently under review as part of KiwiRail's turnaround plan. A new branch line, the Marsden Point Branch, has been proposed to serve Northland Port, a deepwater port at Marsden Point, leaving the North Auckland Line south of Whangarei in Oakleigh.

Three routes of Auckland's suburban rail network make use of the North Auckland Line. From Westfield to Newmarket, it forms part of the Southern Line. From Newmarket to Waitakere, it is used by Western Line services and this section is currently undergoing upgrading. The Onehunga Line branches off the Southern Line at Penrose, where it then follows the Onehunga Branch. Trial commuter services from Helensville commenced in July 2008, but due to patronage lower than expectations, they ceased on Christmas Eve 2009.

The North Auckland Line previously continued to Opua in the Bay of Islands, with the section from Otiria to Opua sometimes known as the Opua Branch. It is now owned by the Bay of Islands Vintage Railway but regular operations have been suspended since 2001, with resumption on a short section of the line in 2008.