Tokyo:A Chinese navy reconnaissance ship entered Japanese territorial waters on Wednesday while tailing two Indian naval ships participating in the trilateral Malabar naval exercise with the US and Japan, a Japanese official has said. A Japanese P-3C patrol aircraft spotted the Dongdiao-class intelligence vessel sailing in the territorial waters to the west of Kuchinoerabu island at around 3.30 a.m., Deputy Chief Cabinet Secretary Hiroshige Seko said. The ship travelled on a southeasterly bearing and left Japanese territorial waters south of the prefecture's Yakushima island around 5 a.m., Kyodo News Agency quoted Seko as saying. "The ship appeared to be tracking two Indian naval ships that were sailing in the waters during joint naval drills" conducted by Japan, the US and India, Defence Minister Gen Nakatani told reporters, according to Kyodo. Japan, the US and India are conducting the naval drills in the waters east of Okinawa, near the Senkaku islands, which both Japan and China lay claim over, since last Friday. According to reports, the Chinese ship also shadowed a US aircraft carrier, John C. Stennis, participating in the joint exercise. Japan has voiced its "concerns" over the intrusion which comes less than a week after another Chinese naval vessel sailed near the Senkaku islands in the East China Sea. The Japanese Foreign Ministry lodged an expression of concern with the Chinese Embassy in Tokyo over Chinese military activities in light of the Wednesday morning incident. "We are concerned about the Chinese military activities" which escalate regional tensions, Foreign Minister Fumio Kishida told reporters. The minister said the Japanese government will continue to take all possible measures to guard and monitor Japan's airspace and territorial waters. China on Wednesday defended the intrusion by its naval vessel into Japanese territorial waters, saying it was an "innocent passage" in line with international conventions. Foreign Ministry spokesman Lu Kang made the comment during a regular press briefing and warned Japan not to play up the situation, according to Kyodo news agency. Last Thursday, a Chinese navy frigate was spotted near the Senkaku Islands in the southernmost prefecture of Okinawa. China lays territorial claim to the islands, which it calls Diaoyu, in the East China Sea. The Japanese government had last week lodged a formal protest after a Chinese navy ship sailed near the Senkaku islands. The Japanese government also summoned the Chinese ambassador over the issue. In 2004, a Chinese nuclear submarine entered the territorial waters near the Sakishima islands in Okinawa prefecture. Although incursions by Chinese coast guard ships in waters near Senkaku are common, this was the first time a navy ship did so. Situated in the South China Sea, the uninhabited Senkaku islands have a total surface area of around seven square km and are believed to be rich in marine and energy resources.