The infrastructure investor Infratil says central or local government must help foot the bill for a proposed $300 million extension to Wellington Airport's runway.
Infratil, which owns two-thirds of the airport, wants ratepayers to contribute more than the $1 million Wellington City Council has already put towards a resource consent application.
Chief executive Marko Bogoievski told shareholders at Infratil's annual meeting it will be difficult to fund otherwise.
"Infratil's obviously interested in a portion of that sort of investment but frankly it is a very hard one to justify on a user pay-type basis so you do have to find public sector - local government or central government involvement - and value somehow these external benefits to see a project like that get finances.
Mr Bogoievski says because of the current length of the runway, more than 400,000 passengers who start their long-haul travel in Wellington then have to go through Christchurch or Auckland.
The council's economic portfolio leader, Jo Coughlan, says ratepayers have to be realistic about helping pay for the proposed extension.
"Given that it is a massive strategic asset that's a very big cost, certainly it would need to be born out over a number of parties and we just have to be realistic that that is how it would have to be paid for."
Wellington Airport says if the runway is extended the tourism generated by a long-haul service would be worth about $44 million a year.