The army denies it has been reckless after two fires were started on the same day during separate training exercises in hot, dry conditions.
By last night a fire had destroyed 350ha of scrub on training land around the Waiouru base in the central North Island after an exercise by Singaporean armed forces.
There were no injuries and no damage to property.
Five civilian helicopters and a Royal New Zealand Air Force helicopter were needed to fight the blaze.
And on Wednesday, a major blaze was ignited by grenade training at the Burnham camp at West Melton near Christchurch.
Selwyn District Council principal rural fire officer Wilson Brown estimated the Defence Force would face a bill of about $200,000 for the cost of tackling the fire.
This morning, acting army chief Brigadier Peter Kelly defended the army's actions.
"This particular fire [Waiouru] clearly was not planned, but it is something that we do prepare for," he told Radio New Zealand.
The blaze was relatively large, but it was not unusual to have fires sparked by training sessions, he said.
He conceded the day was particularly dry, but the training area was isolated and away from any key infrastructure.
"It's essential that we do training in hot, dry climates, we need to replicate those airs of the world we deploy our forces to...we do take a lot of preventative measures but unfortunately... these things do occur," Brigadier Kelly said.
"We are definitely genuinely sorry for the angst and the destruction we have caused the local community at West Melton. We value our relationship with them, we have been in that community since World War II, so we see ourselves as active players in that area."
Brigadier Kelly said they decide on training exercises on a case by case basis and did take weather conditions into account.
"But I can't say we will close off all training ranges because they are so vital to the generation of capability of the New Zealand Army."
The army was conducting an investigation into the fires and would be speaking with the police as part of that.
The police have said arson charges could result if reckless action by the army was proved.
"Reckless would not be a word that I would use to describe this event - it was a carefully planned activity, we felt we had the preventative measures in place, unfortunately a piece of shrapnel skipped out of the containment area that we had set aside for the training area and the strong winds fanned the fire at West Melton."
Defence Minister Jonathan Coleman said he was "very concerned" by the two fires.
Live firing at Burnham has been suspended but the Defence Force could not say whether that decision would be broadened to include other bases around the country.
Dr Coleman could not comment on whether all live fire training should be suspended temporarily as much of the country faced tinderbox conditions.
"I am very concerned about the fires and have been receiving regular updates. I am seeking further information from the New Zealand Defence Force but won't be in a position to comment until I have received it."