"The second nationwide island resource survey is likely to start late this year, helping us to learn about the country's island resources," Lu said.

China will know exactly how many islands it has by the end of 2011, she added.

Xia Xiaoming, researcher of the Second Institute of Oceanography, told People's Daily in February the main causes of the island disappearances are the reclamation of land from the sea, which is sometimes done by filling in the water between the mainland and islands, and by construction projects in which rocks from the islands are used.

Lu said islands help to expand the space people have for economic development, to protect the marine environment, to maintain a balance among species of underwater life and to guarantee the country's security.

Starting on March 1, 2010, a law on island protection went into effect. The law gives China ownership of all uninhabited islands off its coast and calls for a supervision and protection system to be built.

By the end of 2010, the country's surveillance fleet had stopped about 30 instances of illegal development on islands. One case led to the demolition of 15 unauthorized villas in Hongcheng Garden in Ersha Island, South China's Guangdong province, in June 2010.