The Army could be charged with arson after a live firing exercise yesterday went wrong and sparked a large scrub fire, if police believe they were reckless.
Police are working with the New Zealand Defence Force to work out how the fire started at Burnham Military Training Area at West Melton, outside Christchurch.
The NZDF will also be forced to foot the bill for fighting the blaze, police confirmed today.
Soldiers had been doing live firing training, using hand grenades and small arms, went the fire broke out on tinder-box dry scrub land.
The fire took hold quickly, fanned by dry, blustery nor-westers, and it took a massive operation with 60 firefighters and six helicopters with monsoon buckets to bring it under control hours later.
In the aftermath, the police are weighing up their options and assessing whether to pursue criminal charges against the Army.
"The charge of arson is available to these matters if the element of recklessness can be proven," Detective Inspector Tom Fitzgerald, district manager investigations, said.
However the senior officer stressed: "There is nothing, at this stage, to suggest that defence have been reckless. Police understand that they had a fire appliance on site in case of a spark, as they recognised the risk."
The Army yesterday said a live firing training exercise was being held on a gravel area, with a fire appliance on site, when the fire started.
Five houses near West Melton Airport were evacuated and nearby property owners were told to prepare to leave after the fire broke out around noon.
It made its way onto a neighbouring pig farm but was soon contained.
Firefighters feared it would jump Weedons Ross Rd and threaten houses, but they were able to beat it back.
One soldier was hurt trying to put the fire but his injuries were not serious.
Incident controller Sergeant Greg Fagg of the 3rd Emergency Response Troop based at Burnham Military Camp said they had taken measures to prevent a fire from starting, but the blaze had done "exactly what it shouldn't have done".