One person has been hurt and houses were being evacuated as a large scrub blaze fanned by strong northwest winds took hold outside Christchurch.
One Defence Force member was being treated after they were hurt in the effort to fight the blaze, which started around midday north of Old West Coast Rd at an Army firing range.
Their injuries were not believed to be serious.
The thick smoke could be seen as far away as central Christchurch.
The Defence Force said that as well as its own personnel, a number of other agencies were working to keep the fire contained; fire services, helicopters and ambulances were all present.
The cause of the fire was undetermined and would be subject to an investigation.
There had been several fires in West Melton in recent weeks and hotspots from those fires still existed.
The fire covers an area of about 1km by 500 metres and was moving in a northeasterly direction.
Police said five helicopters and 16 ground-based trucks and water tankers were involved in the response.
One flank of the blaze was already under control and it was expected the fire would be contained, police said.
Police have evacuated the Aero Club and an IHC residential property on Weedons-Ross Road, along with several houses in the vicinity.
The Old West Coast Rd was blocked and a no-fly zone was is in place.
Fuel tanks were removed from the aerodrome as a precaution.
The Fire Service said it was too early to say what might have caused the fire.
Local home-owner Angela Huggins said she could see huge plumes of black smoke and was packing her car in case they need to escape.
"At this stage I'm just putting the photo albums and all the irreplaceable stuff and putting a cage in the back for the animals, because if we get asked to evacuate we'll have to go then and there.
"We won't have time to muck around grabbing stuff."
Old Coast Rd resident Kevin Righton, 62, was also fearing the worst and preparing to flee.
"I'm panicking a bit,'' he said. "We're just a kilometre down the road and the wind has really picked up.''
He had his prized classic car, a 1972 Chrysler New Yorker ready to leave.
"I'm waiting to hear what the Fire Service tells me but I won't be sticking around.''
- additional reporting Newstalk ZB