Thousands of Auckland commuters faced widespread disruption on Thursday after a power failure stopped trains on tracks.
The power outage happened just after 4pm at KiwiRail's national control centre in Wellington, affecting all radio contact and signals on the train network in Auckland.
KiwiRail says power has been restored and train operator Veolia says it has restarted services on all lines, but there are likely to be delays on Thursday night.
Veolia says it is confident all issues regarding delays will be resolved by Friday morning's rush-hour.
KiwiRail has apologised for the disruption and says it work throughout the night to find the cause of an electrical fault.
Chief executive Jim Quinn says it is not known what caused it or why back-up systems failed to kick in.
Listen to Jim Quinn