Winston Peters' "cast iron commitment" to move all container operations from Ports of Auckland to Northport has been watered down in the coalition agreement.

On the election hustings Peters said: "The days of the Ports of Auckland as a container ports and as a car yard are numbered". Northport would be handling all of Auckland's container operations by 2027, he said.

The horse trading between NZ First and Labour has led to the commissioning of a feasibility study on the options for moving the Ports of Auckland, including giving Northport serious consideration.

The coalition agreement calls for significant investment in regional rail, but nothing is set in stone to upgrade Northland rail, including a line from Oakleigh to Northport.

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The Auckland Council owns 100 per cent of Ports of Auckland and a council-commissioned Port Future Study recommended the port probably needs to move long term. It recommended the Manukau Harbour or Firth of Thames.

A spokesman for Mayor Phil Goff said the council was progressing work on moving the port from its present waterfront location, but where it goes will need a business case.

Goff supports a wider study and strategy around North Island ports before deciding on relocating Ports of Auckland.

A spokesman for Ports of Auckland said finding the best location, getting consent, funding and building a new port will take decades.

In the meantime the company has developed a 30-year master plan for the port, which will be made public next week, he said.