An independent study on the space needed by Auckland's port has not resolved the quandary facing its owner, Auckland Council.
The council-commissioned study by NZIER found the port's general cargo area was already facing restrictions, and once capacity was reached the port could lose business to rivals.
Debate on the port's future flared last year when the port unveiled plans showing it wanted to extend Bledisloe Wharf by 179 metres into the Waitemata Harbour.
The report is focused purely on the port's operational needs, and will help the council decide how restrictive a planning regime it should seek for the area in the city's Unitary Plan.
The NZIER findings largely reflected the port company's own view that decades of growth could be accommodated by the container terminal at the eastern end, but the general wharves would be too small.
"Those are very old finger wharves designed in a time when ships were unloaded slowly," said the report's author, principal economist Nick Allison. "They are not modern wharves and our view is that you need significant restructuring to make them efficient."
Ports of Auckland said its current thinking is that a slightly smaller extension of around 135 metres might be viable.
NZIER said the problem in the general cargo area was that the ships were getting bigger, needing longer berths and more space for cargo handling as they brought in larger loads.
Forty-five percent of cargo through the general wharves are imported vehicles, and Nick Allison said the port company had yet to find an alternative to parking them on the wharves, even for a short period.
Ports of Auckland has described the NZIER study as a "fair summary".
"This points to the need to extend Bledisloe Wharf through reclamation", it said in a statement.
A leading opponent of harbour reclamation, the downtown business promotion agency Heart of the City, said it was concerned councillors would see the report as a green light to reclamation, without considering effects such as harbour use, the environment, and city views.
The Auckland Council's current position was to seek reclamation deemed a "non-complying" activity in the port area. This would require the port company to go through a lengthy consent process for any further reclamation.
The council must decide whether to maintain this position in submissions it will make to the Unitary Plan, the region's planning blueprint which is before an Independent Hearing Panel.
The council's view will be considered in the next two weeks, with pre-mediation and mediation conferences in March and June.