Hong Kong (CNN) 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 and diminish the stealth capabilities of US submarines.

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.

Tense waters

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 the broadcaster, 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."

Such a system, said Thayer, "mitigates the stealth advantage that submarines have. This would be of direct concern to the United States and other regional states that operate submarines."

Undersea spying

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.

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 seek 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 the relevant Chinese authorities when passing through the designated waters. The draft does not mention how China plans to enforce the law if approved.

"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," said Thayer.