Disruptions to freight delivery can be expected this weekend following the discovery of asbestos in KiwiRail's fleet of DL locomotives.
It is understood 40 - roughly half of the North Island's freight fleet - have been pulled from service after the material was found during the testing of a paint sample.
Chief executive Peter Reidy said all affected staff have been told of the find and while it didn't constitute a health risk, none of the fleet would run again until tests had been done.
"We have made arrangements to continue testing the fleet through the weekend ... We expect confirmation of the results by early next week."
Rail, Maritime and Transport Union spokesman Todd Valster said the find would have a massive effect on rail services. "They are being quarantined as they reach somewhere safe to be parked up, so we don't know if these locomotives can be used in the short term at all."
The Chinese-made locomotives were introduced from 2010, with a contract specification that clearly stated no asbestos.
Questions were raised last year after asbestos was discovered in 10 Australian locomotives manufactured by the same company, but assurances were given that New Zealand's fleet were asbestos-free.
"We are clearly very disappointed," said Mr Reidy. The makers "have undertaken to do whatever is necessary to rectify the situation as quickly as possible."
Asbestos Solutions chief Rick Peebles said the material, to muffle noise, was bonded in a resin in the cabs and in "very good condition".
• It's composed of six minerals, made up of many small fibres.
• It was widely used as a building material until its health effects became known.
• Breathing in fibres from asbestos dust can cause breathing difficulties or even lung cancer.