Auckland commuters face a year of major disruption from Christmas on the southern, eastern, and Onehunga rail lines, KiwiRail said today.

A major $330 million Rail Network Rebuild on the three lines is taking place to pave the way for more commuter trains when the City Rail Link opens, sometime from 2025.

The work will move progressively across the Auckland passenger rail network - starting in early 2023 with the section of the Southern Line between Ōtāhuhu and Newmarket and the Onehunga Line, KiwiRail said in a statement.

Following the usual Christmas/New Year network-wide closure, the Southern Line between Ōtāhuhu and Newmarket and the Onehunga Line will remain closed until late-March. Work will then move to the Eastern Line, which will be closed for most of 2023. KiwiRail and AT are currently working through the schedule for the next sections of work in 2024.

Buses will replace train services with Auckland Transport saying it will promote current services and have ambassadors on site at affected stations to help make it easier for affected passengers. More information about alternative travel options for Onehunga Line and Southern Line customers affected by the first stage of work will be available from November.

KiwiRail chief operating officer – capital projects David Gordon said the work will frustrate commuters, but it needs to be done.

"Given the scale of what we have to do, using our normal evening, weekend and holiday line closures could take decades to get it done. Even closing sections of line but allowing some peak services would push the completion date well beyond the start of CRL operations – which is unacceptable."

Auckland Transport group manager metro services Darek Koper also acknowledged the rebuild will result in "some understandably frustrating disruptions for passengers".

"We are working tirelessly to put in place the best possible alternative transport options for passengers affected by this work.

"Although we do face some extra challenges with the current bus driver shortage, we are working closely with our rail operator Auckland One Rail to make sure we are offering our passengers the most reliable, and regular alternative transport possible in the circumstances," Koper said.

Gordon said the rebuild involves replacing the rock foundations underneath the tracks, some of which haven't been renewed since the Auckland network started being built in the 1870s.

"Like roads, rail lines wear out from use. We've been undertaking routine maintenance and replacing worn-out track and sleepers and we're now moving on to something more fundamental."

Gordon said after the work is complete and CRL opens, Auckland will have a faster, more reliable rail network that will serve passengers for decades to come and help keep Aucklanders moving as the city continues to develop and grow.

He also said that while the majority of the Rail Network Rebuild is expected to be finished before CRL construction is complete, it is likely some lower patronage lines – such as the Manukau to Puhinui line, the Swanson to Henderson section of the Western Line, and the part of the rail network between Newmarket and Britomart (which will see a substantial drop in train frequency once CRL is running) – will be completed after CRL is open.

In a report this year on the governance of the CRL, Auditor-General John Ryan said AT and KiwiRail have signalled that between now and 2036, a further $7.5b will have to be spent on the rail network to realise the full benefits of the CRL.

KiwiRail and AT are developing a business case for this work. Last year, the Herald reported the cost was $6.7b for additional tracks and trains, lengthening platforms for 9-car trains, removing all level crossings on the southern and western lines, and a signalling upgrade.