A damning assessment of the world's biodiversity has found a million animal and plant species are at risk of extinction, largely, because of human activity.

The United Nations-backed report shows nature is declining at rates previously unseen in human history.

Birds around chimney stack Source: AP

One million of the world's plant and animal species are under threat of extinction.

 Of the world's estimated 5.9 million land-based species, the report says more than 500,000 have insufficient habitat for long-term survival.

More than 40 per cent of amphibian species, almost 33 per cent of reef-forming corals and more than a third of all marine mammals are now also under threat.

 In Australia, three native species have become extinct in the last decade and scientists say 17 more could be wiped out in the next 20 years.