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.

Axar.az reports according to state-run broadcaster CCTV, the monitoring networks will cost two billion yuan ($290 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.