The rail line between Ashburton and Washdyke will be out for at least another week after this week's flood damage.
KiwiRail teams are also busy clearing slips on the Midland line, which links Christchurch and Greymouth, with it expected to re-open next week.
South Island operations manager Mark Heissenbuttel said the damage to the line between Ashburton and Washdyke was more severe and cost assessments are still being done.