The Environment Agency believes Muntjac are such a menace it has asked for anyone who spots them to report it immediately. Under the Agency's exclusion strategy and action plan for Muntjac deer the recommended course of action is to eradicate them.
An agency statement said:
A Muntjac Deer Action Plan was prepared by NIEA some years ago which identifies a number of actions to be initiated if a wild population is discovered. This plan has now been activated in an attempt to halt the spread of the species.
The agency has also said anyone who releases or allows the deer to escape into Northern Ireland faces prosecution under the the Wildlife Order (NI) 1985.
There have subsequently been confirmed sightings in County Wicklow and unconfirmed reports from locations across Northern Ireland.
In England Muntjac were introduced into a park in Bedfordshire in the early 20th century and either escaped or were deliberately released. They are fairly widespread now.
Unlike most deer Muntjac don't live in herds but are solitary or found in pairs.