Flights into Queenstown Airport are being cancelled tonight, after air control staff called in sick.
About six flights that were due to fly into Queenstown Airport after 7.30pm have been rescheduled.
A statement from Airways said airlines were making other arrangements for customers on those flights.
Queenstown air traffic control would resume just after 6am tomorrow.
"If you are scheduled to fly in or out of Queenstown from 7.30pm this evening, please contact your airline for instructions," it said.
"Airways has worked through all options to provide cover as normal, and has worked with airlines to investigate whether service could be retained."
The organisation was not able to find a safe solution for the travelling public.
"We've had a few people ask why we can't ring in a controller from another location to cover in Queenstown."
"Because of the nature of air traffic control, controllers need to be trained and rated at each location they work at."
A controller who was certified to work at one airport could not automatically work at all airports nationwide, Airways said.
Queenstown Airport terminal would remain open as normal until 10pm.
Airways extended apologies to affected travellers.