A naval base at Darwin is in lockdown after weapons were stolen from a patrol boat on Friday morning.
The ABC reports an intruder broke into HMAS Coonawarra base, boarded a patrol boat and tied up a crew member at about 1am on Friday. The boat's armoury was broken into.
Police call the incident a breach of national security.
The ABC reports that weapons were stolen, but it is not known how many or what type they were.
An Armidale-class patrol boat would carry a stock of machine guns, assault rifles, shotguns, 9mm pistols and ammunition in its armoury.
Australian Defence Force officers and the Australian Federal Police are assisting an investigation by the Crime and Specialist Support Command.
The base is now in security lockdown. The ABC reports police are at the scene, vehicles are being searched and contractors servicing the base are being turned away.