Officials hope to declare the Auckland suburb of Manurewa fruit-fly free in a fortnight.
A single Tau fly was found in a trap in the south Auckland suburb of Manurewa on Thursday, just weeks after officials finally eradicated the invasive Queensland fruit fly.
The Tau fly, from Asia, is less damaging than the Queensland fruit fly, which was found in central Auckland last year and prompted months of effort to make sure it did not become established.
The Tau fly is a tropical species and therefore very unlikely to be able to establish a population here, the Ministry for Primary Industries said.
However, the species was still a threat to New Zealand's horticultural industry, it said.
A 1.5 km exclusion zone has been established around the site where the fly was found, close to Manurewa High School.
Pumpkins, zucchinis, cucumbers, beans, capsicums, passionfruit and melons, could be taken into the zone, but not out of it.
Senior ministry official Brendan Gould hoped the restrictions would not be in place long.
"If we don't find another fly in the next couple of weeks we would draw the conclusion that it is a single fly - if it is just a single fly, we normally stand [the restrictions] down after 14 days."
The horticulture industry worried that billions of dollars of profits could be wiped out if the pest fly did establish a breeding population.
Horticulture New Zealand chief executive Mike Chapman said the find was very worrying.
The industry was waiting to see what officials might find in dozens of extra traps that were being set out, Mr Chapman said.
"If no more fruit flies are found, that puts a completely different complexion on the situation. But of course, if more are found then it becomes very serious."
The fact the fly was caught in a trap showed the ministry's surveillance programme was working, Mr Chapman said.