China is planning to build a massive underwater observation system across the disputed East and South China seas that experts say could be used to detect the movement of foreign ships.
According to state-run broadcaster CCTV, the monitoring networks will cost 1 billion yuan ($145 million) and "serve as a platform to provide long-term observation data and support experiments in the research of the maritime environments of the two seas."
China is engaged in hotly contested territorial disputes in both seas. Beijing claims almost all of the South China Sea -- parts of which are also claimed by five other countries -- and has built up and militarized many of the islands and reefs it controls in the region.
In the East China Sea, disputed islands have soured relations between Beijing and Tokyo for decades, and led to tense stand-offs between Chinese and Japanese warplanes and ships.
While there is no indication yet that the planned underwater monitoring system is anything but a scientific endeavor, Carl Thayer, a regional security analyst and emeritus professor at the University of New South Wales, said it was "a further unilateral assertion of China's claim to indisputable sovereignty over the South China Sea."
This could anger other claimants, especially if, as Thayer warned, "undersea cables are placed on the seabed in disputed areas or are linked to facilities on any of China's artificial islands."
CCTV's report also suggested that the plan was about more than just science.
Speaking to CCTV, Jian Zhimin, a marine scientist at Shanghai's Tongji University, said the move cemented China's status as an "ocean power."
"An ocean power must be able to go to the high seas and go global," he said. His colleague, Zhou Huaiyang, added the system could provide benefits to "national defense."
Thayer said China "could use the cover story for this undersea network to lay sensors designed to detect the movement of surface warships and submarines in particular."
As China has become more aggressive in pushing its claims in the South China Sea in recent years, other territorial claimants have also pursued militarization.
This month, the Philippines revealed plans were under way to reinforce and upgrade facilities on Pagasa Island, in the Spratly Islands chain.
As well as activity above the water, Vietnam, Malaysia and the Philippines have also reportedly been expanding their submarine capabilities. In the East China Sea, Japan also has a substantial underwater fleet.
Thayer said China's underwater monitoring system could serve the same purpose as the US sound surveillance system (SOSUS), the Cold War-era system used to detect and monitor submarine activity.
In February this year, China State Council issued a draft law to revise its Maritime Traffic Safety Law which if approved, would allow country to prevent foreign ships from passing through Chinese territorial waters.
According to the proposed draft, all foreign submersibles would be required to travel on the surface, display national flags and report to Chinese maritime management administrations when passing through the designated waters.
"From China's point of view it needs accurate information not only on the deployment and patrols of regional submarines, but US nuclear submarines as well," Thayer said.
"This mitigates the stealth advantage that submarines have. This would be of direct concern to the United States and other regional states that operate submarines."