The airport has been closed and all flights, arrivals and departures, diverted to Udon Thani.
Emergency services rushed to Khon Kaen airport, in Muang district, immediately the fire was reported around 7am, said Capt Passakorn Khamphu of the Ban Ped Police.
Police and firemen arrived to see black smoke billowing from Terminal 3.
The fire started on the third floor of the building, with flames spreading rapidly over the roof and along an air-duct system.
Firefighters took more than an hour to extinguish the blaze, using fire retardant foam. More than 40% of the roof was destroyed.
No casualties were reported.
The fire caused a power blackout and the emergency evacuation of more than 1,000 passengers waiting to board outbound flights.
Khon Kaen airport has been closed to all flights, with 16 arrivals and departures affected today.
Provincial Governor Somsak Jangtrakul said it appeared the fire started in an electrical control room on the third floor of the terminal.
Although the fire had been contained and then extinguished, the building remained covered with smoke and other debris, prompting the area to be declared off-limits.
The airport’s passenger check-in system was also affected, causing the temporary closure of the airport.
Governor Somsak said all arriving flights from Don Mueang, Suvarnabhumi and Chiang Mai airports were being redirected to Udon Thani airport, which would also handle Khon Kaen airport's departure flights to Phuket and the three airports.
The provincial governor said he has been unable to confirm when the airport would resume operation as an inspection must be made first to ensure public safety.
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