The items were found by a cleaner at a short-term rental in Keilor East, in Melbourne's north-west, on the morning of January 24.
Police were called to the Belle Vista address about 11.30am, where they confirmed the presence of a number of incendiary devices.
"This was not a run of the mill seizure of drugs and cash – there were incendiary devices and a large quantity of firearms," Detective Inspector Jamie Walker, from the Major Drug Squad, said.
"This is organised crime."
Members of the Bomb Response Unit and the Australian Defence Force attended the property and a number of controlled detonations were carried out, rendering the devices safe.
The rental had been booked for several weeks in January.
Investigators interviewed a man in relation to the booking but released him pending further enquiries.
Another line of investigation surrounds a white Toyota Camry, which travelled to the property several times during the booking period.
On Tuesday, police released CCTV vision of a man filling up the hired car at a service station on the Western Ring Road in Ardeer South on December 25.
The man captured in the footage did not hire the car but police believe he may be able to assist them with their investigations.
Detectives have spoken with the man who hired the car but he has not been co-operative, police said.
Police seized the vehicle on January 24 and it has since been returned to the hire company.
Anyone who recognises the man captured in the CCTV or has relevant information is urged to contact police.
"We will track down those responsible and hold them to account," Det Insp Walker said.
"It would be in your best interests to tell us what you know now."
