The US Navy EP-3 reconnaissance aircraft took evasive action Sunday after a Chinese J-10 warplane zoomed underneath it, slowed down and pulled up in front of it, the Pentagon said earlier.
China's defence ministry said the action of its pilots was "legal, necessary and professional". "The US military aircraft coming near China's border and carrying out reconnaissance has threatened China's national security, damaged Sino-US military air and sea safety, endangered the personal safety of both pilots," it said in a statement.
"The US side should immediately stop such unsafe, unprofessional and unfriendly dangerous military activities and take practical measures to add positive energy to the development of Sino-US military relations."
Pentagon spokesman Navy Captain Jeff Davis said the incident, which occurred west of the Korean peninsula, was an "uncharacteristic" example of unsafe behaviour by the Chinese military.
"There are intercepts that occur in international air space regularly, and the vast majority of them are conducted in a safe manner," he said.
The US accused China of conducting unsafe intercepts twice in May, when similar encounters occurred between a WC-135 "nuclear sniffer" plane and Chinese SU-30 fighters over the East China Sea and later in the month between a US Navy P-3 and Chinese J-10s over the South China Sea.
In April 2001 a Chinese fighter jet collided with a US Navy EP-3 spy plane around 110 kilometres (70 miles) off Hainan Island over the South China Sea.
One Chinese pilot died and the US plane made an emergency landing on Hainan, where China held the 24-member crew for more than a week until Beijing and Washington cut a deal for their release.
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 neighbours and the United States.