As many as 20 wild pigs have been released in South Westland, prompting an immediate cull to eradicate the four-legged "timebombs".
There is speculation a hunter or hunters deliberately released the pigs in the area, which had been pig-free, and in only two weeks they have been spotted around the Paringa River and Lake Moeraki.
The Department of Conservation began a cull three days after the first sighting on June 16, when its hunters shot two boars and two sows.
Four other pigs have been run over, four have been shot by members of the public, and four have been captured and are being held at a farm.
Two more large pigs have been seen, and there are unconfirmed sightings of a sow with piglets.
DOC spokeswoman Cornelia Vervoorn said that under the Wild Animal Control Act, the maximum fine for releasing them was $50,000.
Until June 16, there were no known wild pigs in South Westland, she said.
"Historically there have been attempts to liberate feral pigs in various parts of South Westland and most have failed.
"Feral pigs were present for some years in the low hill country behind Lake Paringa, but we believe this group died out or disappeared a few years ago. There have also been feral pigs in coastal forests and dune areas north and south of the Waiho River from time to time."
Pigs are predators, as they will eat almost anything and have an excellent sense of smell.
They have been known to target invertebrates, Powelliphanta snails, kiwi, weka and nesting seabirds.
There are no kiwi in the Paringa area, but if the pigs wandered further south or north they could reach the Haast or Okarito kiwi sanctuaries.
DOC is keen for the public to call in sightings, and also to let staff know if anyone runs one over: "We need to keep track of how many more might be out there."
There are also concerns the pigs could have come from a Tb-infected area, and could introduce the disease to the large area south of the glaciers.
If they did pass on Tb to possums, the may need to be treated with 1080.
Federated Farmers West Coast president Katie Milne, who has received a few complaints, said they were a "timebomb", and she was "fairly horrified".
- The Greymouth StarBy Laura Mills of the Greymouth Star