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A KiwiRail spokeswoman said yesterday it was installing 1500 new sleepers and 1600m of track as part of the programme.
About 20 staff were working on the programme, which was going to be completed in two phases.
Over the next few weeks, 450m of the upgrade will be completed, and a further 500m completed later in the year, as it moved enough materials to the area.
The remaining 650m would be completed in mid-2018.
"This work will ensure the longevity of the line for many years to come and the undertaking is considered to be one of our larger projects," she said.
The upgrade was expected to cost almost $1 million.