A senior quarantine official has blown the whistle on problems at the New Zealand border.

The Ministry for Primary Industries (MPI) official told Newshub another major biosecurity outbreak is possible because too many detector dog handlers are leaving the programme.

One of those ex-handlers called the environment "toxic", but MPI disputes that.

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Beagles and their handlers are crucial to detecting biosecurity risk items like fruit, plant cuttings, and seeds.

But the anonymous official, who has 10 years' experience in the job, says around half of Auckland's dog handler team has left in the past 18 months due to issues with management.

"It's been pretty well gutted," the anonymous officer says. "There's a lot of experienced staff with a lot of knowledge to pass on that have left. They are feeling frustrated, undermined and devalued."

MPI currently has 32 operational dog teams in Auckland, but since January last year, 17 staff members have left. Of those, seven resigned while the rest moved on to different roles.

"It's a huge number, and it's not something that can be replaced easily," the official says.

But Craig Hughes, MPI border clearance northern passenger manager, says the attrition rate is healthy and denies there's a problem.

"We are back filling, and we know we have the right resources and people in place to deliver what we need to do."

He does, however, acknowledge that some staff members have expressed unhappiness.

"There's some people that are unhappy, I know that. They've told me that."

One woman was a dog handler for seven years, but resigned in December due to roster changes and what she says is the poor attitude of management.

"It was a very toxic place to work, and from what I hear, it possibly is still quite a toxic place to work. As much as I love my job, I'm definitely glad I don't work there now."

She says the frontline handlers and trainers are dedicated professionals, but during her time some faced bullying.

"I definitely know of people that were bullied, very badly bullied by management."

Mr Hughes says MPI has investigated such issues when they were brought to light in the past, and they're looking into "one in particular at the moment".

Newshub has also learned that since large numbers of staff left, the 'green lane' exit at the international terminal is no longer being monitored by dogs between 2am and 5am.

That means passengers on early morning flights into Auckland wouldn't have been checked by dogs.

The whistle blower says that's not ideal when MPI is already grappling with fruit fly, Mycoplasma bovis and the threat of the brown marmorated stink bug, which could decimate fruit crops.

"I think in some respects, it's just a ticking time bomb," says the official. "We are just waiting for something to hit.

"If we get something like foot and mouth disease, you could be talking in excess of $20 billion lost revenue."

But Mr Hughes isn't worried.

"I'm confident we have the right tools and the right measures to meet our biosecurity measures."

Newshub has spoken to another former dog handler who says management told her "if you don't like the roster, you should leave".

But MPI rejects this, and says it has a layered approach to biosecurity which will soon include a trial of new 3D X-ray machines.

Newshub.