But the world’s expanding drone fleets — and the push to weaponize them — have alarmed some academics and peace activists, who argue that robotic warfare raises profound questions about the rules of engagement and the protection of civilians, and could encourage conflicts.

“They could reduce the threshold for going to war,” said Noel Sharkey, a professor of artificial intelligence and robotics at the University of Sheffield in England. “One of the great inhibitors of war is the body bag count, but that is undermined by the idea of riskless war.”

No country has ramped up its research in recent years faster than China. It displayed a drone model for the first time at the Zhuhai air show five years ago, but now every major manufacturer for the Chinese military has a research center devoted to drones, according to Chinese analysts.

Much of this work remains secret, but the large number of drones at recent exhibitions underlines not only China’s determination to catch up in that sector — by building equivalents to the leading U.S. combat and surveillance models, the Predator and the Global Hawk — but also its desire to sell this technology abroad.