China and Japan traded accusations yesterday after Tokyo said Chinese fighter planes had come within 30 metres of its surveillance aircraft.
Japanese Defence Minister Itsunori Onodera termed the events "dangerous", while China warned Japan not to intrude on its naval exercises with Russia.
Japan said Chinese SU-27 fighters came as close as 50 metres to a Japanese OP-3C surveillance plane near disputed islets on Saturday and within 30 metres of YS-11EB electronic intelligence aircraft.
"Closing in while flying normally over the high seas is impossible," Onodera said.
"This is a close encounter that is outright over the top."
A ministry official said it was the closest Chinese warplanes had come to aircraft of Japan's Self-Defence Forces.
Hours later, in Beijing, the Ministry of National Defence said it was the Japanese planes that had carried out "dangerous actions" despite "no fly" notices being issued before the exercises.
"Japanese military planes intruded on the exercise's airspace without permission and carried out dangerous actions, in a serious violation of international laws and standards, which could have easily caused a misunderstanding and even led to a mid-air accident," the ministry said.
It called on Tokyo to stop its surveillance of and interference with the Sino-Russia drill.
"Such actions will increase tensions in the region and could cause a more drastic incident," said Da Zhigang, an expert in Japanese affairs at the Heilongjiang Academy of Social Sciences.
"Both sides should be cautious and restrained."
Tensions have been running high between China and its neighbours over Beijing's land and sea claims.
Beijing lays claim to Japanese-administered islets in the East China Sea known as the Senkakus in Japan and the Diaoyus by the Chinese.
It is also pressing its claims to almost all the South China Sea, brushing aside claims by several Southeast Asian states.
China's proclamation last November of an air defence zone covering disputed islands have raised concerns that a minor incident in disputed areas could quickly escalate.
Back in April 2001, an American spy plane and a Chinese fighter jet collided near Hainan province. The American crew were detained after crash-landing, while the PLA pilot was never found.
China's defence ministry said yesterday the mid-air encounter happened on Saturday morning, as the Sino-Russia navies concluded their three-day drill.
That afternoon, eight ships from both sides fired main guns, high-speed guns and rocket depth charges, Xinhua reported. The two navies also conducted a search and rescue exercise.
Commanders of the two navies are slated to hold discussions on how the drills went today, while the PLA's Zhengzhou missile destroyer and Russia's Varyag missile cruiser are holding an open day for Shanghai residents to check them out.