Opponents of any further extension to Auckland's Queen's Wharf say the council is overstating the benefits for the sake of the cruise industry.
The Auckland Council's development arm, Panuku, wants to build a 90m-long concrete extension, called a dolphin structure, into the Waitemata Harbour.
It says the extension will allow huge cruise ships to berth.
Its project manager John Smith says the number of ships visiting will fall unless the wharf is extended.
He said Auckland was the primary cruise hub for New Zealand but currently available wharf facilities did not provide for the safe berthing of cruise ships larger than 330m.
He says with cruise ships of up to 348m (Quantum class ships) already visiting Auckland and anticipated future visits by ships up to 362m (Oasis class ships), there is a need to provide for extended berthing length to cater for these larger cruise ships.
John Smith expected the smaller ships to be retired and replaced over the next few years.
The lobby group Stop Stealing Our Harbour wants the harbour maintained as it is for future generations.
Its spokesperson, Michael Goldwater, said continuing incursions into the harbour were diminishing its recreational and environmental value.
He said the claims about cruise ship numbers were overstated.
There was a need for an innovative approach, which allowed capacity to be increased using existing infrastructure, he said.
Submissions on Panuku's application are being heard by an independent panel in Auckland today.