Police and other officials were examining the wreckage to find the cause of the explosions, which started in a shipping container used to store fireworks.
Owner Andrew Howard said 20 buildings on the 154-hectare property were razed and 30 others were damaged.
Plans for New Year's Eve fireworks displays in the capitals of three states were now in doubt because of the damage, Howard said.
No workers were at the factory at the time of the explosions, but it appeared that other containers at the site had been tampered with, raising suspicions that someone broke in, police officials said.
"There's a lot of debris and rubble that has to be sorted through yet, to try and find if there are persons inside, but I can tell you there were no people legitimately on the site when the explosion occurred," he told Australian Broadcasting Corporation radio.