A 49-year-old man is facing lengthy prison sentence after a joint operation between the Australian Border Force (ABF) and the New South Wales (NSW) State Police Force cracked an alleged online firearms racket, uncovering a huge arsenal of guns, ammunition, body armour and grenade launchers.

According to authorities on Friday, border intelligence officers became suspicious when they noticed a number of online "firearms-related" purchases headed to a property in the city of Newcastle, 160 km north of Sydney.

As a result, police executed a search warrant for the property on Wednesday and seized "five long-arm firearms, two sound-and-flash grenades, one gas propelled anti-personnel mine, seven gas-propelled grenade canisters, various calibres of ammunition, body armour, camouflage gear, and a hydroponic (drug) set-up with five cannabis plants."

Investigators also seized all the firearms for forensic and ballistic examination.

Charged a string of offences including 11 counts of importing prohibited firearm parts and various other gun and drug charges, the man was refused bail when he faced court on Thursday.

"We have significant intelligence capabilities to detect online purchases of firearms and accessories and through our investigations we have located a number of other serious weapons," ABF Investigations Superintendent Garry Low said.