China rejected two shipments -- almost 546,000 tons -- of U.S. dried distillers' grain, a corn byproduct, because it contained genetically modified material, state media reported Friday.
China's top food-quality watchdog rejected the two shipments because they contained MIR162, a special insect-resistant variety of maize developed by Syngenta, a Swiss maker of seeds and pesticides.
The first shipment, 545,000 tons, was rejected last week in Shanghai, state media said. The second shipment, 758 tons, was rejected Monday.
MIR162 is not on the Chinese government's short list of approved grains considered genetically modified organisms, or GMO.
Still, Chinese consumers remain wary of GMO crops and some nationalist-leaning pundits have suggested the Western-dominated technology leaves China's food supply vulnerable.
The U.S. is the world's largest corn exporter and China is its No. 3 customer. The Asian nation is expected to buy a record 7 million tons of corn in the 2013-14 marketing year.
Chinese authorities said the shipments have been returned and are urging American officials to improve their "inspection procedures to ensure they comply with Chinese quality standards."