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Biosecurity New Zealand director of readiness and response John Walsh said people visiting parts of Otago, Canterbury, Waikato and Bay of Plenty, where populations were known to exist, could play a vital role in stemming the rising population of the "silent pest".
"Left unchecked, they could cover a third of the country over the next 50 years," he said.
Because wallabies tended to hide in scrubland and only came out at night, they could be difficult to spot.
However, people should be on the lookout for telltale signs of wallabies, including droppings or paw prints.
Mr Walsh encouraged people to report wallaby sightings, dead or alive, online at www.reportwallabies.nz.
In recent years, dead wallabies have been found as far south as Palmerston and as far inland as Cromwell and Arrowtown.
A significant number of confirmed spottings have also occurred in the Lindis Valley.
The call for sightings comes as the Ministry for Primary Industries leads the national wallaby eradication programme, which involves an investment of $27.5million over four years.
A wallaby-free country was the ultimate goal, Mr Walsh said.
The economic risk from wallaby infestations was significant, with losses estimated to reach $84million in 2025.
In New Zealand, wallabies are classified as an unwanted organism under the Biosecurity Act 1993, making it an offence to breed, sell or exhibit them without a permit.
Landowners in Otago are required to destroy wallabies on their land where possible, and to report sightings to the Otago Regional Council.