"This is an isolated incident and shows the system working as it should.
"In the last two years around 125 new quarantine inspectors and more detector dog teams are working on the frontline, and we have new x-ray machines installed at our international airports."
Both Labour and the Green Party hit out at the Government, saying the discovery was proof that cuts to MPI had led to "flimsy" biosecurity controls at the nation's borders.
Prime Minister John Key denied the allegations on TV3's Firstline this morning.
"There's been all sorts of changes within the Ministry for Primary Industries, but biosecurity's a top priority and in fact actually the emphasis has changed very much on making sure that we do what we can to stop pests like the Queensland fruit fly.
"But at the end of the day, these things are prolific in Australia, a lot of fruit comes across the Tasman [in] a lot of different ways and so the big job now is to make sure that within that Grey Lynn area that we're very vigilant."
More traps would today be laid in the 1.5km exclusion zone that restricts movement of fruit and some vegetables in Grey Lynn and takes in parts of Western Springs, Mt Albert, Ponsonby and Kingsland.
These traps would be cleared every two or three days, an MPI spokesman said.
The traps contain pheromones that attract all kinds of insects, and each insect has to be examined and identified under a microscope, the spokesman said.
If any Queensland fruit flies are found an announcement would be made and posted online, he said.
Eden Park and Auckland Zoo both lie inside the zone.
The restrictions are likely to be in place for at least two weeks, MPI said. Last year's fruit fly find in Whangarei saw restrictions in place for 20 days, and cost the country almost $1 million.
If no fruit flies are found for 14 days from today the exclusion zone could be lifted.
"These legal controls are an important precaution while we investigate whether there are any further fruit flies present," MPI chief operations officer Andrew Coleman said.
"Should there be any more flies out there, this will help prevent their spread out of the area."
Mr Coleman said the fruit fly probably came to New Zealand in a piece of fruit in an egg or larvae state.
He urged people to abide by the rules, saying previous operations had shown public support "is vital to success".
"We appreciate this will be inconvenient for the many people living in and around the controlled area, but compliance with these restrictions is a critical precaution to protect our horticultural industries and home gardens," he said.
Two Countdown supermarkets sit within the exclusion zone -- on Williamson Ave and Richmond Rd -- as well as a number of other local fruit and vegetable shops.
"It's an inconvenience for our customers but we absolutely recognise that Queensland fruit fly is a serious biosecurity risk and we're happy to help," a Countdown spokeswoman said.
"Customers who live in the quarantine area can still buy fruit and veges from our stores to eat inside the area, but they can't take it from our stores or their homes to anywhere outside the controlled area."
More than 90 staff are also collecting samples of fruit from home gardens in the area to test for any flies or their eggs or larvae.
Mr Coleman said a mobile field laboratory would be in action later today to analyse fruit collected and also inspect any insects found through the trapping. First results from the trapping and fruit analysis are not expected until tomorrow morning.
He said people found to be taking fruit or vegetables out of the exclusion zone could be prosecuted under the Biosecurity Act.
The maximum penalty for anyone prosecuted is $50,000 fine or three months imprisonment.
The maximum penalty for a company is $100,000.
"But we've never had to prosecute anyone and don't anticipate having to do that this time," Mr Coleman said.
"I'd like to thank the people of Auckland for their co-operation in this response. Compliance with these restrictions is a critical precaution to protect our horticultural industries and home gardens."
Auckland Zoo said the restrictions would not have any impact on bringing food in for the animals, but it was working with MPI on the disposal of waste fruit products.
A spokesman for the Cricket World Cup said MPI would supply specialist bins for fans to dispose of fruit and vegetables after the match between New Zealand and Australia on February 28.
The weekly Grey Lynn Farmers Market also falls within the cordon, but manager Louise Carr-Neil said it would still go ahead this Sunday.
Grey Lynn Residents Association committee member Nicola Legat said she was concerned about the "economic impact on our local businesses", and said everyone was "anxious" about how long the restrictions would be in place for.
Horticulture New Zealand president Julian Raine laid the blame for the fruit fly breach on "Australia's inability to control the pest" and urged the reinstatement of mandatory luggage x-rays at airports.
"It is not acceptable to go through this drama every summer. New Zealand horticulture deserves better protection."
Labour's spokesman for primary industries Damien O'Connor said the fruit fly discovery showed there was a "failure" at New Zealand's borders, and blamed Government cuts for leaving MPI short of experienced staff.
