Chinese ships and aircraft have probed the sea and air borders of Japan and South Korea on hundreds of occasions over the last 18 months, with analysts suggesting Beijing is testing the response times and the resolve of Washington's two most important security allies in the region.
And with China ramping up its claims on Taiwan, analysts anticipate intrusions and confrontations will increase.
The South Korean government confirmed in early October that Chinese military aircraft made more than 70 unannounced entries into its air defense identification zone during 2021.
Concern was also raised when a fleet of Chinese warships last year traversed the narrow Tsushima Strait — the stretch of water separating the Korean Peninsula from Japan — to carry out exercises with Russian vessels.
South Korea also operates an ocean research station close to Socotra Rock, also known as Ieodo, a submerged sea mount that is 149 kilometers (92 miles) from the Korean island of Marado, but China has repeatedly laid claim to the waters surrounding the platform, which is 287 kilometers from the nearest Chinese territory.
Japanese dispute
Japan is also embroiled in disputes over sovereignty with Beijing.
Chinese coast guard ships have repeatedly intruded into Japanese territorial waters surrounding the Senkaku islands, known as Diaoyu Islands in China, a chain of five uninhabited islands in the East China Sea that Beijing insists are rightfully its territory.
Japan's military has in the past detected Chinese surveillance and surveying vessels in its waters off the southern prefecture of Okinawa, as well as unidentified submarines.
Experts have suggested that the Chinese military has attempted to identify deep-water channels that will permit its submarines to sortie into the Pacific Ocean more safely in the event of a conflict breaking out.
Japan was similarly alarmed when China fired ballistic missiles into Japan's exclusive economic zone surrounding Okinawa when Nancy Pelosi, the speaker of the US House of Representatives, visited Taiwan in early August.
Beijing claims Taiwan is a province of China that will eventually be reincorporated into the mainland — by force if necessary — and analysts suggest the missiles that landed in Japanese waters were intended as a warning.
'Intimidation pattern'
Taken with the overt threats made towards Taiwan, they say the incursions and testing of nations' ability to respond are effectively a pattern of intimidation aimed at the countries best equipped to resist any offensive moves by Beijing in Northeast Asia.
"In all these contested waters, China is trying to create a 'new normal' and to make sure that everyone knows their forces are there," said John Bradford, a senior fellow specializing in maritime security at Nanyang Technological University in Singapore.
"When it comes to the Senkakus, for example, the terms of the US-Japan security treaty states that the islands are under Japanese control, but if China can undermine that idea by having ships operating in those waters, then that weakens the credibility of Japan's position," he told DW.
The Chinese incursions are also designed to test the reactions of the Japan Self-Defense Forces, he said, while militaries "always like to train in the areas they expect to be fighting in," to enhance tactics and determine supply requirements and other elements of being at war.
Trilateral alliance
The trilateral alliance of the US, Japan and South Korea poses the biggest challenge to China's territorial ambitions in Northeast Asia, so Beijing cannot expect to simply occupy areas without meeting resistance, as it did in the disputed atolls and reefs of the South China Sea less than a decade ago.
An official of the National Institute of Defense Studies in Tokyo said China is again trying to employ the "salami-slicing technique" that has served its territorial ambitions in the past, laying claim to more areas of ocean and then the land, disputing their territory with the legitimate governing nation and weakening the resolve or ability to defend it.
"China's behavior is based on its desire to eliminate any country that it sees as a rival and, unfortunately, it is inevitable that we will see more of the same sort of aggression aimed at Japan, the US and South Korea," said the official, who declined to be named as he was not authorized to speak to the media.
James Brown, an associate professor of international relations at Temple University's Tokyo campus, pointed out that a strong military presence pushing at the extremities of its borders serves to demonstrate that Beijing "can make life very difficult for its neighbors, if it wants to."
"South Korea and Japan both have very limited natural resources and rely heavily on China for trade, so they have to be constantly concerned with resisting but not antagonizing Beijing so much that it retaliates in the trade sphere," he said.
THAAD dispute
That is precisely what happened when South Korea deployed the advanced Terminal High Altitude Area Defense (THAAD) weapons system in order to deter North Korean ballistic missile attacks. Beijing demonstrated its opposition by banning Chinese nationals from vacationing in South Korea, dealing a devastating blow to the nation's tourism sector.
"This approach works," Brown pointed out. "When Pelosi visited Seoul after being in Taiwan, President Yoon [Suk-yeol] basically hid and declared that he was not available to meet her in person because he was so afraid of the reaction from Beijing."
"So as a combination of military and political pressure has already been shown to be effective, it is inevitable that China is going to employ the same tactics in the future," Brown said. "It's a challenge."