Natural gas fields lie in waters where Chinese, Japanese and Taiwanese claims overlap, near a tiny group of islands known as Diaoyu in Chinese and Senkaku in Japanese.
China has finished building a series of lighthouses and stone tablets on islands and reefs off its coast to delineate its territorial waters in the disputed East China Sea, Xinhua news agency said on Tuesday.
Natural gas fields lie in waters where Chinese, Japanese and Taiwanese claims overlap, near a tiny group of islands known as Diaoyu in Chinese and Senkaku in Japanese.
By building "permanent structures" on islands, countries can help extend their territorial waters and exclusive economic zones under international legal protocols governing the sea.
China's latest lighthouse at Waikejiao, a tiny speck off the coast of Jiangsu province, was the last of 13 structures built to mark its territorial baseline, Xinhua said, citing Captain Zou Xingguo, political commissar of the Chinese navy's East Sea Fleet survey team.
China claims that a straight line drawn between the points should be the starting point for determining its territorial waters, Xinhua said.
Japan has also built facilities including a lighthouse on Okinotori, also known as Douglas Reef or Parace Vela, which it calls its southernmost island. China refuses to recognise Tokyo's claim, saying it is a rock, not an island.
China's project to build base points extends to the Paracel Islands, known in Chinese as Xisha, southeast of Hainan Island in waters claimed by Vietnam.
China's nautical boundary claims are particularly controversial in the South China Sea, an important shipping route and oil-rich area where several countries'' claims overlap.
Neighbouring countries have had brief naval clashes over reefs and sandspits known as the Spratley Islands, located about 900 km south of China's shores.
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