An intruder robbed an Australian navy vessel of a cache of weapons after overpowering military personnel on guard, the defence department said, in an unprecedented security breach.
The Australian Department of Defence said the infiltrator "overwhelmed a duty member onboard a patrol boat" which was moored at HMAS Coonawarra, a naval base in the northern city of Darwin.
"The intruder overpowered the duty member, accessed the vessel's armoury and removed a number of weapons," it said in a statement, without specifying what arms were taken.
"The person then departed the vessel with the weapons."
Reports said firearms usually found on an Armidale-class patrol boat could include machine guns, assault rifles, shotguns and 9mm pistols, as well as ammunition.
The Australian Broadcasting Corporation said a single intruder armed with a gun tied up a crewman in the attack, which took place at the Larrakeyah Naval Base, which was later placed in lock-down.
"Police received a report just before 1:00 am that a Defence member had been assaulted and a cache of weapons had been stolen from a navy patrol boat moored at the base," Northern Territory police Commander Richard Bryson said.
"Police have locked down the base with all vehicles exiting being searched."
Navy chief Vice Admiral Ray Griggs ordered an investigation into security on all naval ships and bases in the wake of the incident, which was also being probed by the Australian Federal Police.
"It's certainly a breach of security and it's a very concerning one for me," Griggs told Fairfax radio, adding that it was the first breach of its type on an Australian navy vessel.
He said the assaulted crew member had his life threatened but was recovering well.
About 600 naval personnel are based in the Darwin region, many working at sea in border protection.
Tropical Darwin is a key defence hub for Australia, with rotating United States Marines based in barracks outside the city since April this year as Washington looks to deepen its presence in Asia.