A fire broke out in a forestry block on Wednesday afternoon in the Lee Valley near Nelson.
Nine different brigades and helicopters with monsoon buckets were fighting the fire.
However, all six helicopters were grounded on Wednesday evening after a drone was seen in the area.
The fire has burned through about 5 hectares of pine forest - threatening 11 homes which have been evacuated.
Fire and Emergency New Zealand (FENZ) incident controller Steve Triggs said drones "were a safety risk to aerial firefighting, as a mid-air collision with a drone could have fatal consequences".
"The drone sighting has completely impacted helicopter operations," Triggs said in an update just before 8pm. "Firefighting efforts are on hold until the safety of air operations can be assured."
Civil Defence has set up an evacuation centre at the Wanderers clubrooms in Brightwater.
"The fire is burning over about 5 hectares of a pine forestry block and is not yet contained. Firefighters are unable to continue the firefight using ground attack while the helicopters are grounded because the terrain is too steep and dangerous," FENZ said.
"Eleven houses on River Tce between the Lee Valley Bridge over the Wairoa River and Mead Rd have been evacuated by police."
