Japanese nationalists landed on the disputed island on Sunday, provoking strong protests from both the government and the Chinese people.
The Japanese move, in response to a group of Chinese activists landing last week on the islands that belong to China, comes as the United States stepped up efforts to increase its military presence in the Asia-Pacific region. This will complicate the regional situation, Chinese analysts said.
About 150 Japanese lawmakers and members of right-wing groups arrived on Sunday morning in waters off China's disputed island to "mourn soldiers who died in World War II". Ten nationalists then landed on the islands, waving Japanese flags, Kyodo News Agency reported.
The landing, the third of its kind by Japanese nationalists within the year, is the latest Japanese attempt to display its so-called sovereignty over the islands. The disputes over the islands have been fanned after Tokyo Governor Shintaro Ishihara initiated a plan in April to purchase the islands from their so-called Japanese owners.
Beijing on Sunday summoned the Japanese ambassador to China, Uichiro Niwa, to lodge solemn representations over the landing and urged Tokyo to "properly handle the issue and avoid seriously damaging China-Japan relations".
Protests broke out in more than 10 Chinese cities, including Chengdu, Sichuan province, Xinhua News Agency reported.
The protesters marched on major roads, gathered around main Japanese landmarks and waved Chinese flags. They shouted "Defend China's territory" and "Japan, get out of the disputed island!"
One Japanese government official expressed his concern to Kyodo that the landing by the nationalists may lead to a situation that is difficult to resolve.
Zhou Yongsheng, an expert on Japanese studies at China Foreign Affairs University, said it is understandable that the Japanese move aroused anger.
The sentiment displayed by protesters will influence Chinese policymakers and Beijing may take a tougher line with Tokyo, Zhou said.
But Feng Zhaokui, a Japanese studies researcher at the Chinese Academy of Social Sciences, said that diplomacy should not be "hijacked" by public opinion.
Disputed island: Japan, US to hold sea exercise
Japan plans to replace its ambassador to China, possibly in October, the Japanese newspaper Yomiuri Shimbun said.
Niwa had been under pressure from both ruling and opposition parties to resign for misrepresenting Japan's position when he warned, in June, that the Tokyo prefectural government's plan to buy the disputed island could spark an "extremely grave crisis" between China and Japan.
The decision to replace the ambassador indicates Tokyo will adopt a stronger stance, analysts said. "Tokyo, of course, prefers someone who can better deliver its tough position," Zhou said. In another move that analysts said may further complicate the situation, Japan and the US will hold a joint military exercise in the western Pacific on Tuesday.
Japanese newspaper Sankei Shimbun quoted a source at Japan's Defence Ministry as saying that the drill is aimed at the disputed island.
In view of China's "growing presence" in regional waters, Japan hopes to boost its capability to defend its "remote island territories", the newspaper said.
Washington is enhancing ties with its allies in the Asia-Pacific region as part of its "return to Asia" strategy.
Washington may use the tension over the disputed island to boost its military presence in the region, analysts said.
Li Hong, secretary-general of the China Arms Control and Disarmament Association, said the US is seeking to beef up the confidence of its Asian allies by holding various drills, and Japan is also trying to use drills to "normalize its military forces".
Li said China and Japan should cool down over the islands dispute, but added it was Japan's unilateral attempt to change the status quo of the islands that led to rising tensions.
Earlier this month, Washington and Tokyo agreed on a proposed second revision of a Japan-US defence pact.
The pact was released in 1978 and first revised in 1997, and the Sankei Shimbun said the second revision is preparing for unexpected incidents in the East China Sea.
Li Xiushi, a researcher on Japanese studies at Shanghai Institutes for International Studies, said the US and Japan may use the tension over the disputed island to "make specific designs" for the revision.