Auckland City Council is preparing to tear down what remains of a former freezing works in Penrose, which was gutted by fire before Christmas.
The fire started in a derelict coolstore on 20 December and the last fire crew left the site on Sunday. It will be handed over to the council in the New Year.
Deputy chief fire officer Roger Callister says the destruction of the site will make it difficult for investigators to determine the cause of the fire.
Southpark Corporation, which owns the former works, says the clean-up will be a lengthy one and will cost millions of dollars.