Ni Lexiong, director of the Sea Power and Defence Policy Research Institute at the Shanghai University of Political Science and Law, says the Chinese military may have been reacting to provocation by Japanese naval vessels, Hong Kong's South China Morning Post reports.

BBC: Japan Maritime Self-Defense Force destroyer Yuudachi

Ni Lexiong, a military naval expert at the Shanghai University of Political Science and Law, believes China's alleged radar moves were a "face-off" between the two countries and "a warning to Japanese vessels", South China Morning Post reports.

BBC: China media: Pyongyang warned