A concept drawing of the City Rail Link's Aotea Station near the Wellesley/Albert St intersection

Tens of thousands of Auckland bus passengers will have their trips through the city centre changed from Sunday as preparations begin for construction of an underground train station.

Trips through the heart of the CBD could become five to ten minutes longer, due to the diverting of 26 bus routes around the year-long closure of the Wellesley Street/Albert Street intersection.

It is the biggest downtown bus shake-up for years, with diversions affecting up to 145 buses an hour, and some 60,000 passengers on a weekday.

Chris McKeen/Stuff Work has started on the southern-most part of the City Rail Link project at Mt Eden earlier this year, marked by Auckland Mayor Phil Goff, CRL CEO Sean Sweeney and Transport Minister Phil Twyford.

Auckland Transport expects some anxiety for a week or so as passengers adjust to the re-location of some bus stops, but the agency doesn't believe patronage will be affected.

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The changes are needed as preparatory work begins on the 300m-long underground Aotea Station on the City Rail Link.

RYAN ANDERSON/STUFF Rail tunnel works along Albert St will move several blocks north in March, closing the intersection with Wellesley Street.

Bus routes from the west, central Auckland and North Shore are affected, including the high-frequency Outer Link service.

On the upside for bus commuters, new sections of bus priority lanes are also being introduced on downtown routes such as Queen Street, and Hobson Streets.

The new bus lanes will be permanent, in a move which Pete Moth, the manager of network development, said was "an opportunity to change behaviour" giving more of the limited road space to buses instead of cars.

RICKY WILSON/STUFF Buses will take a new way around the closed Wellesley St/Albert St intersection until early 2021

The need to make changes around Wellesley Street was a "catalyst" to introduce the new bus priority measures at the same time.

There will be changes to a further four bus routes in a year's time, when the Wellesley/Albert Street intersection is due to re-open, but the nearby Albert and Victoria Street intersection will close.

Mayoral Drive behind the Aotea Centre will be closed until CRL opens in 2024.

Supplied/Auckland Transport 26 bus routes will take a detour until early 2021 around the closed Wellesley/Albert St intersection

Pete Moth, Manager Network Development said the affected bus services come from west and central Auckland, and some from the North Shore.

The closures will be the last time some of the roads are seen in their current form, with upgrades to Albert Street and proposed changes to Victoria Street, meaning they will have few general traffic lanes, and more space for pedestrians, cyclists and buses, when they re-open.