Auckland commuters face delays on Thursday evening as limited train services resume after a power outage knocked out the rail network in New Zealand's biggest city.

A power outage at KiwiRail's national train control centre in Wellington about 4pm affected all signals and radio communications on the Auckland rail network.

Train services across the city were suspended, causing delays for commuters as they headed home from work.

Rail operator Veolia says all signals were restored just after 5pm and limited services are resuming on all lines.

However, it's warning commuters that the delays are expected to continue until at least 8pm.

People are still being advised to take alternative transport home.

Meanwhile, KiwiRail has apologised to Aucklanders for the outage.

KiwiRail chief executive Jim Quinn says an urgent investigation is under way to determine the cause of the outage.