The Earth is undergoing a sixth mass extinction, with scientists warning that the “biological annihilation” of wildlife is "more severe than perceived".

Blaming the overpopulation and over-consumption of humans, the researchers said the world had a window of about 20-30 years at most to tackle the crisis.

"Earth is experiencing a huge episode of population declines and extirpations" - when a species is wiped out in a particular location - "which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilisation," the researchers wrote in the journal Proceedings of the National Academy of Sciences.

"We describe this as a 'biological annihilation' to highlight the current magnitude of Earth's ongoing sixth major extinction event."

In the study, researchers from Stanford University and the National Autonomous University of Mexico examined the population trends of 27,600 vertebrate species such as birds, amphibians, mammals, and reptiles, including a detailed analysis of 177 species of mammals.