China's reported construction plan on an island in the South China Sea is totally an issue within Chinese sovereignty, Foreign Ministry spokeswoman Hua Chunying said on Monday.

Hua made the comments in response to a report about China's reclamation plan on the island.

Observers said China's construction plan, if true, is primarily to improve people's living conditions there and its ability for humanitarian work.

According to a report by the South China Morning Post, China is looking to expand its biggest installation in the Nansha Islands into a fully formed artificial island, and the proposal has been submitted to the central government.

Philippine Foreign Affairs spokesman Charles Jose said the Philippine government will lodge a formal protest if the report on the proposed artificial island is true, Philippine media reported.

Wu Shicun, president of the National Institute for South China Sea Studies, said better infrastructure on such islands is badly needed to improve civilians' and soldiers' livelihoods.

After the expansion, more supplies will be available, and humanitarian rescues in accidents like the disappearance of Malaysia Airlines Flight MH370 will be facilitated, he said.

It is unnecessary for countries like the Philippines to make a fuss over the issue, given that China lags far behind other countries in terms of the scale and speed of infrastructure construction in the South China Sea, he said.

In another development, the Foreign Ministry also denounced the "joint activities" by the Philippines and Vietnam on one of China's Nansha Islands as "a clumsy farce".

Philippine and Vietnamese military personnel on Sunday played soccer and volleyball on Nanzi Island in the South China Sea, illegally occupied by Vietnam.

"We demand the Philippines and Vietnam stop stirring up quarrels and troubles, strictly abide by the Declaration on the Conduct of Parties in the South China Sea and not complicate or spread the disputes," Hua Chunying said.

Chen Qinghong, a researcher on Philippine studies with the China Institutes of Contemporary International Relations, said Manila and Hanoi aim to flare up the "China threat" by displaying a show of "unity", but their differences in claims of sovereignty in the South China Sea are likely to stop them from maintaining long-term ties, he said.

[email protected]