The Fire Service says bad weather have caused the fire that has destroyed a store in the Hokianga township of Opononi.
The owner of the Four Square shop noticed smoke coming from the ceiling of the old wooden building as he was cashing up on Sunday night.
By the time he'd raised the alarm the store was ablaze and fire crews from surrounding areas were unable to save it. No one was hurt in the incident.
Fire safety investigator Craig Bain believes stormy weather on Sunday may be to blame.
"The area of origin ties in with where the mains electrical cable comes in. What we're possibly picking is that yesterday's adverse weather with very, very heavy rain and high winds has pushed some water in through the roofing iron and it's created an arc which created the spark which started the fire."
Post boxes melted
The fire melted 114 post boxes attached to the store. New Zealand Post says it will try to salvage any mail that might have survived, but it is unlikley to be fit for delivery.
A street posting box next to the store appears undamaged and the contents will be checked on Tuesday.
Mail for Opononi box-holders will be available from the nearby Omapere Post Centre until further notice.