China defended on Thursday its drills in East China Sea, saying that its naval ships out in the East China Sea did not violate international laws and posed no threat to other countries.
Japanese media have alleged that two Chinese submarines and eight destroyers were spotted circling Japan's Okinotori coral reefs.
Ministry of National Defense spokesperson Huang Xueping said it is routine practice for the army to have its drills in the high seas, and is also a practice done by other countries.
"Countries concerned should not track down or disrupt the activities of Chinese military vessels engaged in normal defense exercises," Huang warned.
Japan complained to China on Wednesday that a Chinese military helicopter flew close to a Japanese naval vessel, the second encounter of such nature to happen in a month, news agency AP reported.
Japan's defense ministry said the helicopter was within 300 feet (90 meters) of the Japanese vessel and had circled it twice. The Japanese vessel was monitoring Chinese military activities.
However, Japanese Foreign Minister Katsuya Okada said on Wednesday the Chinese vessel did not violate any international laws, the Kyodo News reported.