Water being dropped from monsoon buckets to fight a huge fire on the Remarkables, in Queenstown, is vapourising before it hits the flames.
Department of Conservation community relations officer Nick Edwards said all efforts last night were being concentrated on a small area of the blaze, which prevailing winds were threatening to push south.
Te Anau helicopter pilot Richard "Hannibal" Hayes, working with night-vision goggles, was the lone unit tackling the blaze from the air once darkness fell.
Earlier in the day, up to five helicopters were fighting the fire, which by last night had spread over about 250ha.
The fire began on adjacent farmland owned by Dick Jardine.
Mr Jardine was conducting a permitted, controlled burn-off when the fire spread to conservation land about 2pm.
Mr Edwards said it was not yet clear how the fire got out of control.
"Once we've got it out, then we'll sit down and have an investigation into that," he said.
DoC fire crews had been unable to do anything since darkness fell, since the land was too steep and rugged for fire appliances and the smoke and the rugged terrain made it unsafe for helicopters not equipped with night vision.
Mr Edwards said most of the fire was blazing up the mountains, towards the snow line and was not of too much concern.
"But we've got one particular hot spot that we're worried about," he said.
"It has the potential to spread down, and then we would have a huge fire."
Flames were reaching 10m to 15m high when they hit a dry patch of the brush and scrub covering the mountainside.
The fire was not threatening any property, and Mr Edwards said wind was blowing smoke away from the Remarkables skifield.
Heliworks manager Dave Kershaw said last night that the fire could spread a further 5km south towards Wye Creek, between Queenstown and Kingston.
"Basically it goes from lake level to 5500 feet [1676m]," he said.
"If the gods were smiling very kindly on us tonight I'd say it might not spread, but that's unlikely."
The scrub was so dry and the fire so hot that water was having a limited effect, Mr Kershaw said.
"And because the hillside is so steep, we can't put people up there."
Mr Kershaw said fire crews would be back at first light to see how best to tackle the fire.
- NZPA
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