The incident occurred Sunday when the two Chinese J-10 warplanes intercepted a US Navy EP-3 reconnaissance plane in international air space west of the Korean Peninsula, Pentagon spokesman Navy Captain Jeff Davis said.
One of the Chinese jets came underneath the US plane at a high rate of speed then slowed and pulled up in front of it, he said.
"It was forced to take evasive action to prevent the possibility of collision," Davis said.
Davis added that the incident was "uncharacteristic" of the normal safe behavior of the Chinese military.
The East China Sea is part of the Pacific and home to small islands whose ownership is disputed by China, Japan and Taiwan.
China also claims a string of islets across the South China Sea and its military expansion in the contested waterway has sparked heightened tensions with regional neighbors and the United States.
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