6 November 2015 Last updated at 22:58 GMT
The collision, involving a low loader vehicle, happened on Mullaghduff Road as the policeman was investigating the theft of an ATM near Newry.
Police said the lorry was driven at speed directly at the officer and he was pinned between it and a police vehicle. The lorry left the scene.
Police are treating the incident as attempted murder.
Colletta Smith reports.
An on-duty police officer has been seriously injured in a hit-and-run incident in Cullyhanna, County Armagh.