Six helicopters are being used to fight a burn-off on farmland that got out of control about 10km from Te Anau in Southland.
Fire and Emergency NZ was alerted to the fire in the Mt Prospect area about 2.30pm on Friday, says spokeswoman Sally Chesterfield.
The fire initially covered about 300 to 400ha but has spread to more than 1000ha.
Chesterfield said the fire isn't threatening any buildings as it is located in a very unpopulated area, a long way from any buildings or sheds.
It started on farmland and has spread to scrub on Department of Conservation land.
The fire is spreading in hot, dry and windy conditions and it's too dangerous to put ground crews in.
"We don't have it under control in any way," she said.
"Helicopters are just tackling it from the edges and it is still running."
Chesterfield said crews would continue to fight the fire until dusk, but would then have to postpone efforts until the morning due to safety reasons.
"Crews won't even come close to putting the fire out this evening, unless it were to burn itself out," she said.
She said ground crews would monitor the fire overnight, with controls beginning again first thing in the morning.