Tension between Asia's two biggest economies is heating up as both countries build up their militaries and boost maritime activity.
On Tuesday, Japan again criticised China for sending ships into waters around the disputed Senkaku Islands, which China calls the Diaoyu Islands, in the East China Sea. Tokyo said it was the 11th time this year "Chinese government ships have been spotted entering Japanese territorial waters off the islands".
But compared with the long-running island dispute, in which Beijing mostly sends coastguard vessels, separate Chinese warship activities near Japan are more alarming from Tokyo's perspective.
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Three Chinese warships - the Lhasa, a Type 55 guided-missile destroyer, destroyer Chengdu and replenishment ship Dongpinghu - were spotted on Tuesday in the Izu Islands south of Tokyo, according to Japan's defence ministry.
The Chinese warships had been operating in partnership with five Russian warships since June 12, the ministry said, but there was no confirmation from Russia and China they were coordinating with each other.
Japan was then prompted to send a Maritime Self-Defence Force flotilla to 11 Indo-Pacific countries as part of joint naval exercises with the US and its allies to counter a more assertive China, according to Kyodo news agency.
China has been sending warships to waters near Japan since late last year. In November, a Chinese naval ship sailed in Japan's waters off its southwestern prefecture of Kagoshima, the first such movement since July 2017, Kyoto reported, citing Japan's defence ministry.
During exercises in May, the Chinese aircraft carrier Liaoning launched fighters near Japan and the carrier was later shadowed by Japan's Izumo helicopter destroyer in the western Pacific.
James Bosbotinis, a specialist in defence and international affairs, said Chinese warships were bound to sail deeper into the ocean as the PLA Navy (PLAN) became more advanced.
"As the PLAN develops it is venturing further afield and to access the northern Pacific, for example, requires transiting through the Sea of Japan and the Tsugaru Strait," he said. "There is also a lot of signalling, though, on the part of Beijing with its naval deployments around Japan, and driven by Japan's position on Taiwan, cooperation with the US and a perception in China that Japan is working with the US to contain it."
Besides the island dispute, many new geopolitical factors have added strain to the China-Japan relationship. The ongoing debates in Japan over raising defence spending and potentially developing nuclear-powered submarines will be viewed with concern in Beijing.
Japan hosted the Quad summit in Tokyo late last month with the aim of pursuing a free and open Indo-Pacific. However, the Chinese foreign affairs ministry labelled it "a real threat that destabilises peace and cooperation by forming a small circle and inciting confrontation".
Japan has become more vocal in support of the self-ruled Taiwan, an island Beijing sees as a core interest. In June last year, Japan's deputy defence minister, Yasuhide Nakayama, said in a conference "we have to protect Taiwan".
Mainland China and Taiwan split in the late 1940s because of a civil war when the Kuomintang was defeated by Communist Party forces and fled to Taipei. Beijing sees the island as part of China and has never ruled out the use of force to take control of it.
Bosbotinis said China's increasing military power and its activities around Japan were the principal driver for Tokyo to consider enhancing its military capabilities.
"[An] increased Chinese presence around Japan and cooperation with Russia will result in stronger defence cooperation between Tokyo and Washington, and between Tokyo and other regional states and minilateral groups," Bosbotinis said.
According to news reports, Japan is developing its own long-range surface-to-air cruise missile and rail gun-based counter-hypersonic weapon system. It is also modifying the Izumo-class destroyer to operate the F-35B fighter.
Timothy Heath, a senior security analyst from US think tank Rand Corporation, said China was probably sending its ships near Japan to both carry out military training and to send a signal about Chinese resolve and strength.
"Beijing could be sending the ships near Japan as a response to Japanese patrols in the South China Sea as well as US and allied naval activity near Taiwan and the South China Sea. While Chinese military activity is sure to anger Tokyo, Beijing may conclude it has more to gain politically with its own populace by sending ships near Japan in retaliation for the naval activity near China by the US and its allies," he said.
Heath added that he did not expect to see provocation from Beijing or Tokyo.
Grant Newsham, a senior research fellow at the Japan Forum for Strategic Studies, said China was intimidating Japan.
"Not necessarily to occupy Japan, but to psychologically dominate Japan to the point Tokyo cannot act independently ... And when the Chinese Communists make some demands on Japan, Tokyo will have no choice but to comply," Newsham said.
This article originally appeared in the South China Morning Post (SCMP), the most authoritative voice reporting on China and Asia for more than a century. For more SCMP stories, please explore the SCMP app or visit the SCMP's Facebook and Twitter pages. Copyright © 2022 South China Morning Post Publishers Ltd. All rights reserved.
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