The fire was under control by 5.30am and crews remained on scene to dampen down hotspots and ensure the shed did not reignite.
“There is no mention of what the damage to the shed was,” Munn said.
No one was injured in the fire.
Specialist fire investigator Andrew Cotter said the cause of the fire was an electrical failure.
“It was an unspecified electrical fault.
“It could be something like a wiring fault or water getting into the electrical system.”
Due to the amount of damage, the specific fault was not able to be determined, he said.
“Due to the location and distance from the fire stations, it’s taking a significant amount of time for the fire brigade to get there.
“It appears the fire’s burned for quite a while before it’s been noticed.”
Cotter said it was important for people to regularly check electrical systems, especially in commercial buildings, to prevent faults that could cause fires to start.
Eva de Jong is a reporter for the Whanganui Chronicle covering health stories and general news. She began as a reporter in 2023.