The fire that ripped through a Mitre 10 centre and storage shed in Onehunga on Monday is being treated as suspicious.
Mitre 10 CEO Craig Wilson said a report from the fire service had ruled out "electrical and accidental factors" as the likely cause of Monday's blaze.
The general manager of the Mitre 10 store said he was stunned by the report's findings.
"We will be stepping up our security procedures across the business to continue to safeguard our staff and employees," said Mr Grove.
Manukau District Chief Fire Officer Larry Cocker said efforts to get into the site to find the cause yesterday were slowed as insurance assessors and investigators needed to go through the scene with firefighters.
- NZHERALD STAFF