Auckland's commuter trains are running again after a breakdown caused major delays and threatened to disrupt travel plans for people heading to Jonah Lomu's public memorial service.

A train broke down at Otahuhu at 8.16am on Monday, and caused significant hold-ups as services on three lines were cancelled.

Auckland Transport said commuters should expect further hold-ups as services returned to schedule.

WATCH: Stuff will livestream the service for Jonah Lomu from midday

The southern, eastern and Onehunga services into the central city were suspended while the broken-down train, which blocked the tracks, was removed.

Auckland Transport (AT) staff worked to get the trains running in time for the memorial service, which kicks off at Eden Park at 1pm.

An AT spokesperson said restoring services to help people get to the Lomu memorial was the organisation's "main priority".