Auckland Mayor Phil Goff wants Auckland's port to move so the public can reclaim access to the waterfront, he says - but he wants evidence it will work.
A recent report recommended Auckland's port operations be moved to Whangarei in Northland at a cost of $10 billion, but the report has sparked heated debate.
Mr Goff told Morning Report on Tuesday: "I concur with Prime Minister Jacinda Ardern that it's not a case of if but when, but in order to move that port we need to do that on an evidence-based provision of analysis."
He said before the last general election, he called for analysis that looked at what was best for Auckland, the upper North Island, and the country.
"I wanted a report that was based on evidence and we have seen a lot of stuff emerge from that [recent] report that doesn't answer some of the vital questions.
"Why do I want the port to move ultimately? Because I want to get public access back to the waterfront. And we think that there are alternative uses for that land.
"But we have to look at the whole picture. And this report is not looking at the whole picture. The whole picture says, you know, what is the best area for the port to move to and the assumption seems to be made at the start of this working party's process ... 'we'll move it to Northport and we'll try to justify it' ...
"It's $10 billion and we need to know - the government will need to know, before they invest in the biggest infrastructure project anywhere in the country - that that is going to provide value for money for Auckland, the region and the country.
"Once you've got the facts, and not simply a biased approach to this - you know, trying to find the facts that will suit a conclusion but actually examining the facts and finding what conclusion comes from that ... then you can make the decision, but I think we all need to be satisfied about that."
Education Minister Chris Hipkins was standing in for Prime Minister Jacinda Ardern on Morning Report on Tuesday morning.
"The report hasn't yet come to Cabinet. So we need to take some time to digest it when it does. Obviously the government has been clear that we think this is something that we do need to be talking about. The prime minister has been clear it's a question really of when a decision on this has to be taken. But we want to make that decision based on evidence.
"I think the argument that Phil Goff raised is a very valid one, which is that this is a very big decision. And we have to carefully work through all of the economic impacts of that, all the environmental impacts of that, the flow-on consequences to other areas and other parts of the economy.
"We've got to work our way through all of those things very carefully, we've got to make those decisions based on robust evidence. And in any case, you know, like this, there's going to be different views, the advice is going to be contested."
He said the government would always look for more evidence.
"So we've got a report we'll be looking at, you know, testing out what's in that report, seeking further advice and further information based on that. And then obviously, we'll have more to say on that once we've had the opportunity to do that work."
Mr Hipkins said he agreed with Ms Ardern's view on the port.
"I think that there's real merit in looking at it. I think the growth at the Port of Auckland is very constrained... simply put, they can't expand much further where they are, there's going to be a need for expansion and there's also the you know, public's desire to get better access and reopen access to the waterfront."
Despite former Prime Ministers Sir John Key and Helen Clark joining forces on the lobbying for the move, and Trevor Mallard supporting it, Mr Hipkins said: "I think that support is all well and good, but the government's ultimately going to make decisions based on what the evidence and the facts tell us rather than who's supporting us.
"I think it's really important that we take our time to make sure that the decisions that we made [were] based on a very, very robust analysis."