The Government's new goal of exterminating every rat, stoat, possum and feral cat from New Zealand by 2050 has been described as a "game-changer".

Prime Minister John Key announced the formal target yesterday, calling it the most ambitious conservation project in the world.

At the heart of the policy is a new $28 million joint venture, Predator Free New Zealand Limited, which will identify large-scale pest eradication projects and attract private investment to boost their reach.

Sir Rob Fenwick, chairman of the Predator Free New Zealand trust and a leading advocate for pest eradication, said it would allow a military-level response to the problem for the first time. "It's a real game-changer. This fund will drive a more strategic and comprehensive approach to a landscape-scale assault on predators that we haven't seen before."

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The policy is largely dependent on private funding, prompting Labour and the Greens to question whether the Government was doing enough.

Green Party conservation spokesman Kevin Hague pointed to a University of Auckland study which put the cost of a predator-free New Zealand at $9 billion. Through the new joint venture, the Government will put in $1 for every $2 contributed by businesses and charities.

Fenwick said philanthropists - including the Morgan Foundation and the Tindall Foundation - were "lining up" to invest in biodiversity projects.

To help achieve the target, the Government is also betting on the development of a major scientific breakthrough by 2025, capable of wiping out one of the key predators - rats, stoats or possums.