The NSW Department of Primary Industries said on Tuesday that 480 beekeepers were in a 10-kilometre eradication emergency zone established around the Port of Newcastle to control the mites, as part of a six-month emergency biosecurity order issued on Sunday.

About 240 hives had been destroyed so far, a department spokesperson said.

Agriculture Minister Dugald Sanders said on Tuesday night that the deadly mite had been discovered in bee hives at three more properties - in Newcastle, Seaham and Bulahdelah, 100km north of Newcastle. The discovery at Bulahdelah means a second biosecurity zone had been established around the NSW Mid-North Coast town.

The earlier emergency order stated that "varroa mite was detected at two properties in Mayfield and Mayfield West" on June 22. The mites were originally detected in "sentinel" hives at the Port.

By Sunday, varroa mite had been "detected at several properties across NSW, and it is suspected to be present at several other properties".

Asked if beekeepers destroy the hives themselves, the department said: "No, bees must be euthanised and hives destroyed by NSW DPI staff. If you have bees and hives in this zone, you must make them available to NSW DPI staff".

Australia had been the only significant honey-producing country to be free of the varroa destructor mite.

Previous biosecurity research, produced by Plant Health Australia, said the "varroa mite has never been eradicated from a country before".

"Therefore, if varroa was to enter Australia, it would need to be detected rapidly to provide the greatest chance of successfully eradicating the pest. The most likely entry pathway for varroa mites into Australia is by accidentally introducing infected honey bees on ships or shipping containers."

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Honey bees from overseas had been previously intercepted at various Australian ports. The reddish brown oval-shaped mite is the size of the head of a pin. It has caused international concern among beekeepers for 50 years, having spread from the Asian honey bee to the European honey bee in the 1970s. Virginia Tech university research noted that varroa destructor was "believed to be the leading cause of colony collapse" in European bees, "with the exception of Australia and several isolated island locations".

The mite had caused a "near-global epidemic", causing billions of dollars in losses and severely threatening bee-colony survival.

The mite causes a parasitic disease called "varroosis" that leads to colony collapse by weakening host immunity and spreading viruses. It has developed resistance to pesticides used to kill mites and ticks.

More sustainable pest control methods have been used, as standard chemical methods became less effective. The contamination of honey with pesticides is also a concern.

For every year Australia remains free of varroa mite, industries reliant on honey bee pollination receive a huge financial boost, the Plant Health Australia research found.

Australia has a large population of wild honey bees that provide "free pollination services" to agriculture and horticulture. This means that pollination of crops often occurs "without any deliberate intervention from, and at no cost to, the grower".

"It is generally accepted that varroa mite will eventually become established in Australia. When it does, varroa mite is expected to progressively kill 95 to 100 per cent of Australia's wild honey bee population, greatly reducing the free pollination service they provide.

"As the number of wild honey bees falls, and the impact on the honey bee industry is felt, the horticultural and agricultural industries will be severely affected."

The department said it was working with industry to "closely monitor" the pollination issue.

Since the introduction of varroa mite to New Zealand, wild bee colonies have disappeared and pollination costs soared - including for kiwifruit.