Three people suffered smoke inhalation, Deputy Gov. Fikret Kasapoglu said, but there were no other casualties in the blaze, which spewed thick black smoke high into the air. Authorities gave various possible causes for the fire, including a spark from a welder's torch or a short-circuit.
There was no sign of terrorism or sabotage, said Vedat Muftuoglu, another deputy governor.
Hundreds of uniformed cargo workers who escaped the building in a panic were anxiously watching the blaze meters (yards) away from the building.
A large section of the cargo building that housed warehouses of major cargo companies collapsed, Kasapoglu said. The damage could affect cargo flights to Istanbul, the AP reports.
Kasapoglu assured passengers that there was no danger and flights were taking place, although with delays.
Planes dropped water onto the flames, and airport authorities said the fire was slowly being tamed.
Private NTV television said the blaze began in a section where fuel depots were located. Airport director Irfan Balta said planes had been successfully moved away from the danger area.
The cargo building is used to store international cargo arriving in Istanbul. A hangar housing military aircraft is located nearby.
Russia has deployed two armies and three units of Airborne Forces to its western borders as part of a verification check, Russian Defense Minister Sergei Shoygu said