Four helicopters and 15 appliances are battling a large blaze near Nelson.
Ten hectares of grass and gorse was alight and wind was spreading the fire, southern fire communications shift manager Jan Wills said.
The Fire Service was called to the blaze in Dodson Valley, near suburban Atawhai, just before 4pm today.
An ambulance was called to the scene to tend to a firefighter suffering smoke inhalation, Ms Wills said.
His condition was not known but he was not thought to be seriously injured.
The fire was near a residential area but no one had been evacuated.
Local resident Stuart Morrison told NZPA the fire "got big in a hurry" but was moving away from the residential area because of a wind change.
"They (firefighters) seem to have got the better of it."
He said there were "a lot of flames" visible and the smoke was being blown towards the city.
"It's spectacular watching the choppers lining up (to refuel)."
Mr Morrison and his family had not been warned they may have to evacuate and were not worried because the wind was blowing the fire away from their house.
A no-fly-zone was declared in the area for all non-emergency aircraft.
