Major excavations are starting in Auckland's Mount Eden as work begins on connecting the Western railway line to the under-construction City Rail Link.
A four-metre-wide trench is being dug along Fenton Street near the closed Mt Eden station to relocate the Huia Two watermain as part of the construction.
Link Alliance said relocating the pipe will be a significant undertaking.
Officials estimate the job will take three months to complete - given the size of the trench and how close it is to a live rail corridor.
Link Alliance and Watercare will work together to minimise disruption to those living and working near the site.