A report's been leaked recommending Auckland's port be moved to Manukau Harbour, instead of Northland.

Former Far North Mayor Wayne Brown is the chair of the Government group reviewing the future of three major North Island ports.

He says his group interviewed 80 industry bodies and delivered two interim reports, in public, on time and within an 800-thousand dollar budget.

Now, Brown's frustrated Transport Minister Phil Twyford has spent more money on this other 'secret' report, which he says makes the bizarre recommendation to make Manukau Harbour the port.

He says it's a shallow harbour with a dangerous sand bar at the entrance and no land on the shore for a port study.

He told Heather du Plessis-Allan that his report was written by people with expertise in road, rail, sea freight and infrastructure - whereas this report was done by people with expertise in health economics. 

Brown says that they looked at Manukau Harbour and moving the port there is "just stupid".

"Shipping goes down the other side of the island. All the ships go from China through to South America."

However, Auckland Mayor Phil Goff says that it makes sense to move to Manukau.

He told Heather du Plessis-Allan that most of the freight arriving in Auckland goes South anyway, so it makes sense to have it delivered there.

Goff admits that it is a challenging harbour, but he says that every port needs dredging.

"Those are challenges that, according to this report, can be overcome."

He says that no other report except for Brown's report was in favour of a move to Northport.