The man who headed the working group on the future of Auckland's port says all three options for its location have major flaws.
The downtown port is running out of room, and the Port Future Study has identified Manukau Harbour and the Firth of Thames as possible locations to replace it.
Opponents have said a port off the west coast would be impractical and potentially difficult to navigate, while one in Thames would require major infrastructure such as rail and road upgrades.
The independent chair of the group, Rick Boven, said the members were divided over which option they preferred.
"If you look at the three live options, you'll find that there are major flaws for all three. And our challenge is to find the best, among a number of unattractive options."
Mr Boven said a lot more investigation was needed to decide which option worked best.
Employers and Manufacturers Association chief executive Kim Campbell said the new port faced huge infrastructure costs which could not be matched by the current port's profits.
He expected the port could take up to 50 years to build.
"No matter how successful the port is, it will never be able to move in the manner that this report suggests, so there will [need to] be other funding streams."
The port project would need major international investment, he said, and although many people wanted to invest in ports it was unlikely there would be great interest yet because of long timeframes and planning issues.