Finance Minister Grant Robertson has warned there will not be a quick, cheap or easy answer to the question of Ports of Auckland's future.

Sir John Key and Helen Clark are backing the government working group's recommendation to relocate port operations to Whangarei.

But former minister Steven Joyce said relocation would be unfeasible, given available infrastructure.

Grant Robertson told Newstalk ZB the port will need to relocate or radically change, and the Government won't be rushing into any decision.

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He said the port won't remain competitive as a deep sea port, in its current form, beyond the 2030s.

"Whether or not the answer is to move the operations to North Port is the big question.

"What are the other logistical changes that are needed? Do the costings stack up? And is the only alternative?"

Robertson said the Government has not ruled out any option, but every available option is likely to be expensive.

"This won't be a cheap endeavour, I can assure you of that.

"You can have to look at the long term here. We have to look at what is the place in the upper North Island to complement the Port of Tauranga that already does a huge turnover."

Yesterday, Key told Newstalk ZB's Mike Hosking it made no sense to keep the port in the CBD, when there are other good ports not far away.

He said Tauranga's port was rapidly growing and Northport could handle the extra load.

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"You'd four-lane the highway to Whangarei, and you release an enormous amount of land down on the waterfront which then Auckland Council owns," Key said.

Key said selling the land would scratch an "enormous" amount of debt off the council's balance sheet, and allow the waterfront to be used far more effectively.

"World class cities with a waterfront like we've got, don't lock it away with big red gates and take hundreds of trucks through town every day."

Key said some estimates put moving the port at $10 billion, while others say the cost of keeping it in the CBD tallies up to $8b.

"The differential between the two is not insubstantial - probably a few billion - but not nearly as big a number I think as some people say."