Visitors arriving at New Zealand's main tourism gateway could be greeted by the stench of rotting food waste once a new composting plant begins operating nearby, claim campaigners.
But the company behind the plans says the expansion of its facilities will actually reduce odour discharge.
Living Earth, a subsidiary of Chinese-owned Waste Management, was issued resource consents just before Christmas for the continuation of green waste processing and the construction of a food composting facility on Puketutu Island in the Manukau Harbour, about 5km away from Auckland Airport.
The consents were granted on a non-notified basis so the public did not have a say.
Living Earth has been turning garden waste into compost on the island since 2007, but residents who have campaigned against existing food composting facilities in other parts of the country claim the processing of kitchen waste is a far smellier process.
Geoffrey King has been a vocal opponent of a Living Earth composting facility in the Christchurch suburb of Bromley, which has processed food waste since 2009.
He said a foul odour from the plant could be detected for up to 10km.
"Food protein such as processed food, meat, dairy products and fish create an offensive odour when placed in material for composting purposes," King said.
He said the planned Puketutu Island plant, which isn't expected to begin operating until 2018 at the earliest, could cause odour problems for local residents.
"But worst of all the Auckland International Airport is close by and I believe it will be within smelling distance of this operation," King said.
"Imagine overseas visitors arriving and getting a whiff of the offensive odour these plants give off in our supposed clean green country."
More than 4 million international passengers arrived at Auckland Airport in the year ended November 2015.
An Auckland Airport spokesman said the company had not been consulted during Living Earth's resource consent process and would not have expected to have been.
"Without more information about the planned food composting process, we are unable to comment on the possibility of this impact," the spokesman said.
Tuakau resident Judy Halsey, who has railed against a food composting facility run by another company in the Waikato town, described the smell as "like a garbage bin".
She also claims odour from the Puketutu plant could be detectable within a 10km radius around the island.
But Waste Management's general manager for technical services Dave Perkins said this was incorrect.
"As we have stated before, the smell of compost -- a natural earthy smell -- is not detectable beyond the island," Perkins said. "This will not change with the consent approval."
Perkins cited a independent expert report conducted by Terry Brady Consulting for the resource consent process, which said the expansion of Living Earth's facilities on Puketutu would result in a 30 per cent reduction in odour discharge.
It was Living Earth's view, he added, that the smell emitted from the Christchurch facility was "non-offensive" and "naturally earthy".
"In-vessel processing [planned for Puketutu] eliminates any need for concern from Auckland Airport," he said.
Residents living near the island have expressed concern that the expansion of Living Earth's operation was given consent without public input.
Perkins said Waste Management received written approval from parties including the Mangere Bridge Residents and Ratepayers Association, Villa Maria, iwi and Watercare.