A remote and windswept biodiversity hot-spot in New Zealand's subantarctic islands has been formally declared mouse-free, after one of the most sophisticated pest eradication projects in the world.

The Antipodes Islands, about 760km southeast of Bluff, were once home to about 200,000 mice that preyed on bird chicks and eggs, invertebrates and plants.

The impact was enough to alter the biodiversity of the 2100ha island group, recognised as a World Heritage site for its outstanding natural values.

Fears had grown after mice were observed eating alive large seabird chicks in their nests on two south Atlantic islands.

The Antipodes Island wandering albatross is among 25 seabird species that breed there. Photo / Kath Walker/DOC
The Antipodes Island wandering albatross is among 25 seabird species that breed there. Photo / Kath Walker/DOC

It wasn't known whether that was happening on the Antipodes, but the behavioural shift was seen as a risk for all 25 bird species breeding there.

As of today, however, that threat no longer exists.

The islands have been formally declared rid of the scourge by the Department of Conservation's Island Eradication Advisory Group.

It was largely thanks to the "Million Dollar Mouse" project - a fundraising effort in which the public contributed $250,000, WWF NZ provided $100,000, and the Morgan Foundation matched donations dollar for dollar.

The rest of the money came from Island Conservation and the Department of Conservation (DoC).

The five-year project involved preparations and hut repairs, a helicopter bait-drop in June 2016, and post-eradication monitoring by just-returned teams that searched the island for a month and found no sign of mice.

"The success of this project was built on the lessons and experience from many other island eradications in New Zealand and abroad," DoC project manager Stephen Horn said.

"The subantarctic islands are remote, but the role they play in global conservation as the home for so many unique species can't be overstated."

Conservation Minister Eugenie Sage said its success meant 21 species of breeding seabirds, more than 150 species of insects, 21 uncommon plant species and four unique and endemic land birds could now thrive.

"This is huge news for conservation both in New Zealand and internationally," said Sage, who recently visited the island aboard HMNZS Wellington.

"The successful Antipodes Island mouse eradication is another landmark conservation achievement which underlines DoC's technical expertise in pest control and threatened species protection."

The project follows other successful large-scale pest eradications on New Zealand islands.

Elsewhere in the subantarctics, Campbell Island was cleared of rats in 2001, rabbits and mice were eradicated from Enderby and Rose islands in 1993, and a small population of goats were swept from Auckland Island by 1992.

More recently, DoC eradicated cats and rats from Great Mercury Island in the Hauraki Gulf in 2014, and eight mammalian pests were eradicated from Rangitoto and Motutapu Islands in 2009, including rats, mice, cats and stoats.

More than 100 of New Zealand's 220 large islands are now pest-free, which the Predator Free 2050 initiative aims to replicate across the mainland by the middle of the century.