Britomart train station in central Auckland has been shut today after KiwiRail found significant cracks.
KiwiRail says it knew of some faults near Britomart and was already planning to deal with them, but last night it found they needed immediate repairs.
The cracks are caused by pressure from trains passing over the rail and are called Rolling Contact Fatigue.
KiwiRail said staff have been on site all morning, and work to repair the track faults is underway.
However, it expects the station to shut for the remainder of the day and to reopen tomorrow morning, with more work set to take place on Friday evening.
KiwiRail is in the midst of a six-month programme – which started a month ago – to repair or replace about 100km of rail.
It expects most of the work to be completed in co-ordination with scheduled temporary line closures for four weeks at a time.
KiwiRail said that alongside Auckland Transport, it would also look into why the wear and tear problem on the tracks was more prevalent in Auckland than elsewhere.
Both agencies would consider all possible contributing factors, which KiwiRail noted has internationally been linked to derailments.
Chief operating officer Todd Moyle said they would continued to assess rail across the network to understand the extent of damage and what areas to prioritise.
“We are also closely monitoring locations where damage is already known and work scheduled to ensure we can still operate trains safely through those areas.
“In the meantime, our priority is getting the rails fixed which we want to do a planned way but from time to time, when circumstances demand, there may be unscheduled interruptions, like today.”
Meanwhile, a four-week temporary closure of the Eastern Line will end on Sunday, with 17km of new rail laid. And starting from Monday, trains will be replaced by buses on the Southern Line between Newmarket and Penrose for four weeks for a rail upgrade.