A huge fire engulfed the cargo section of Istanbul's Ataturk International Airport on Wednesday, temporarily disrupting air traffic and causing thousands of people to flee, authorities said. 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 huge black cloud came, it smelled like cables burning, the roof started burning," cargo worker Omer Toplar said. "There was no explosion." 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. 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. "The fire is under control and we're taking precautions to prevent it from spreading to passenger terminals," said Baris Tozar, the undersecretary of the Transportation Ministry. "There are no problems concerning flight security," Tozar added. 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. Private Sky-Turk television reported occasional explosions. Earlier, private NTV television said some cargo workers may have been trapped inside the two-story cargo building but authorities denied the report. Radical Islamic, leftist and Kurdish militants are active in Istanbul and Kurdish militants recently claimed responsibility for a major fire at an Istanbul factory.