The Nanhaijiu 118 takes part in a drill off the Xisha Islands on May 3. [Photo by Liu Xiaoli/China Daily]

"The lighthouses sometimes serve as temporary shelter to sailors from toppled ships. We found some quilts at the lighthouses - people apparently slept there. ... Also we saw some toppled ships that were stranded there," another source said.

Skeptics have questioned the amount and quality of China's maritime navigational aids for ships in the South China Sea. But both the visible and radio aids conform to international norms and are available to civilian ships, and China's services help protect the maritime ecology, the sources said.

"If a ship carrying hundreds of thousands of tons of crude oil sinks here, it will be a disaster and the pollution will impact both China and other areas," one of the sources said.

China, a member of International Association of Lighthouse Authorities and the International Maritime Organization, subscribes to international standards, follows the systems stipulated by the associations, and enjoys a rising reputation within them, according to a source.

"China, a responsible major country, makes great efforts to ensure navigational safety - not just our own but also the world's. We do not oblige other countries to follow us, but we are indeed improving navigational safety and environmental protection."

What's been built

China has built a number of lighthouses in both the Xisha and Nansha islands to help boost navigational safety in the South China Sea, a critical maritime and trade corridor linking the Pacific and Indian oceans.

On Oct 9, a completion ceremony was held for the construction of the Huayang and Chigua lighthouses on Huayang Reef in the Nansha Islands, marking the beginning of China's civil aids to navigation in the area. On Oct 21, Sansha city in Hainan province announced that two Xisha lighthouses - on Jinqing Island and Lingyang Reef - were complete, China News Service reported. In April, a lighthouse on Zhubi Reef in the Nansha Islands area also was completed.

zhangyunbi@chinadaily.com.cn