Shippers have given the thumbs down to one finding from the Port Future Study - that Auckland's next major port could be sited in the Manukau Harbour.
The study, officially due out today, said Auckland's next new "super port" could be moved to the Manukau Harbour or the Firth of Thames at a cost of $4 billion to $5.5 billion.
New Zealand Shipping Federation executive director Annabel Young, who is a member of the Consensus Working Group launched by Mayor Len Brown a year ago to reconsider Ports of Auckland's place on the city waterfront, said shippers do not favour a west coast port alternative.
Young said the working group included a diverse range of people but they had reached an agreement.
"And the agreement that we reached did not assume that the port would have to move, but if it does need to move it needs somewhere to go to, and we need to start thinking about that now," she said.
The Firth of Thames was originally considered as the site of New Zealand's only oil refinery, which ended up being built at Marsden Point, near Whangarei.
Young said it was no secret that shippers favoured a port on the east coast - where most of New Zealand's ports are located - because of the generally wilder weather and sea conditions on the opposite coast.
"The east coast is always going to beat out a west coast site," Young said. Manukau has scored well because of its proximity to road and rail. "That said, it's not a great site for a port," she said.
Hear Annabel Young speaking to NewsTalk ZB's Early Edition with Rachel Smalley:
Shifting sands and a difficult prevailing wind made the Manukau a difficult choice.
"Anyone who has ever taken a ship in there just laughs at it being turned into a major port, but more work needs to be done," she said.
Gerard Morrison, the New Zealand managing director for Maersk Line - the world's biggest shipping company - said the existing port did not have the land area to handle future growth.
"The one thing that is certain and definite is that the current port of Auckland will not be able to handle the task in the future," he said. "Whether it is 10 years away or 20 years away, they are going to struggle for space," he said. "So an alternative of some description has to be found."
Morrison said Manukau could be a viable option "but the question would be at what cost".
David Vinsen, chief executive of IMVIA, an industry group representing the used car import business, said car importers had an "agnostic" view of where the future port should be.
"We are relatively agnostic about where the cars arrive, but there are some strong indications as to why they should continue to stay in Auckland," he said. "It's also the time and money aspect, and the practicality of moving them elsewhere."
New Zealand imports about 250,000 cars a year - mostly through Ports of Auckland. The report said Northland has been rejected because of the difficulty transporting cargo across Auckland city to rail and road hubs in the south.
Daniel Silva, the secretary of the New Zealand Importers Institute, said the estimate of $4 to $5.5 billion "appears to be optimistic".
"The obvious solution is to incentivise the port to optimise and rationalise its operation in co-operation with other ports, unencumbered by petty parochialisms," Silva said. "The alternatives amount to grandiose schemes to relocate the port, totally ignoring the reality that in New Zealand, these days, we just don't do massive infrastructure."
• When the current port runs out of room two sites are possible: The Manukau Harbour, Firth of Thames.
• The cost: $4 billion to $5.5 billion.