The Government won't be revealing where and when Ports of Auckland will be moving when it makes an announcement about its future this week, Prime Minister Jacinda Ardern says.

Infrastructure Minister Shane Jones will on Thursday release a major report into the future of the North Island's main port and the Government's recommendations.

Ardern this week told reporters Cabinet had decided it was "not viable" for the port to remain in Auckland and that it was a matter of "when", not "if".

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But speaking to Newstalk ZB on Tuesday, Ardern said no decision had been made about where the port would be moving.

"You will get an indication of the additional analysis that needs to be undertaken to make a decision that is to the value of billions of dollars, so we need to make sure the analysis is robust," she said.

"We need to do extra work."

Moving Auckland's port to Northland was mooted in the report as the best solution, with details leaked earlier this year.

It concluded Auckland's current port operations are "no longer economically or environmentally viable".

The relocation has been called New Zealand's most ambitious infrastructure project ever, costing $10 billion and including a $1.6 billion rail line to Marsden Pt.

• Part 1: The Big Idea

• Part 2: For and against: Why move the Auckland port?


• Part 3: The lure of the Waikato: Why not go south?

• Part 4: The North of Plenty: The prospects for Northland

• Part 5: Crunching the numbers to shift the Auckland port