"The boys on the first appliance did a great job fighting it until reinforcements arrived," he said.
Two Kaitaia crews and one from Ahipara doused the fire, which covered an area of roughly 15m x 15m, and got back to bed about 5.30am. Crews from Mangonui and Okaihau were called out but stood down before they reached the mill.
Fire investigator Craig Bain said one building measuring about 3m x 3m was razed and three others were badly damaged. The mill's main building was still standing, as was one other structure.
The fact there was no power to the site, and that it was just the latest of a series of early morning fires at the mill suggested it had been deliberately lit.
"It didn't catch fire by itself," Mr Bain said.
He urged people to keep out of the old mill because of the danger posed by tanalising chemicals in the burnt-out buildings. Northland Regional Council staff were to inspect the site today.
Kaitaia police were also at the scene yesterday.
The site had been used as a wrecker's yard until 40 car bodies went up in flames early on June 12. In April, a Portacom-style cabin, used as a smoko room, was destroyed by fire. In March a car body was set alight.
Call Kaitaia police on (09) 408 6500 with any information.