Results of tests on KiwiRail's new Chinese-made locomotives for asbestos are expected today.
Forty of the state-owned company's locomotives were taken out of action following the discovery of the potentially deadly material in a soundproofing compound inside one of the vehicles on Thursday.
Samples were taken from locomotives in Auckland, Hamilton, Tauranga and Palmerston North over the weekend, and from locomotives in Wellington yesterday, KiwiRail said.
They were then analysed by an accredited laboratory in Wellington.
"Our preliminary advice following testing of a first locomotive on Friday indicted that the asbestos in that locomotive was contained and does not constitute a risk to health," KiwiRail chief executive Peter Reidy said.
"However the health and safety of our staff must be our priority so we need to have analysis of all the DL locomotives before we can determine what our next steps will be. That analysis is being completed this afternoon so tomorrow we should be in a position to consider our next steps," he said.
The manufacturer has accepted responsibility for the issue and indicated that they will do what is necessary to rectify the situation, Mr Reidy said.
Testing was carried out as soon as the manufacturer confirmed the presence of asbestos in the soundproofing compound, which is not exposed and either coated with paint or sealed beneath panelling, he said.
Asbestos can be harmful when fibres become airborne.