MANILA - China's reported plan to build a military base on an artificial island at the Fiery Cross Reef, known in the Philippines as Kagitingan Reef, could undermine the Philippines' arbitration case, a Department of Foreign Affairs spokesman said Monday.

DFA Spokesman Charles Jose said the Philippine government has yet to confirm the report, which first came out in the South China Morning Post.

"If the report is true, very clearly what China is doing is - it intends to alter the status quo and change the character of the feature and we believe that by doing so they will prejudice the arbitration we have filed against China before [the United Nations Convention on the Law of the Sea]," Jose said in an ANC interview.

If confirmed, he said the Philippines will lodge a protest before Beijing.

Jose said the Philippines is working with its partners and allies in the region to protect its territorial and maritime interests and ensure the freedom of navigation in the waters of the South China Sea. He said the Philippines is working with the Association of Southeast Asian Nations for the creation of a Code of Conduct in the South China Sea and has recently forged the Enhanced Defense Cooperation Agreement (EDCA) with the United States.

"Hopefully, that will strengthen and advance our external and territorial defense. Of course, we are also trying to cooperate with our partners like Japan, South Korea and Australia," he said.

The South China Morning Post earlier reported China plans to construct an artificial island with all supporting installations like air and sea ports. The island would be constructed on the Fiery Cross Reef, known in the Philippines as Kagitingan Reef, the report said.

Jin Canrong, a professor of international relations at Beijing's Renmin University, said the proposal has already been submitted to China's central government.

He said the artificial island would be at least double the size of the US military base of Diego Garcia, a 44-square-kilometer American military base in the Indian Ocean.

Analysts say China's move indicates a shift from defense to offense in the East and South China Seas.

It is also seen as a step to the declaration of an air defense identification zone.

Analysts warned reclamation at the Fiery Cross Atoll, which is claimed by China, the Philippines and Vietnam, would further strain Beijing's relations with neighbors.

The Philippines earlier said it was investigating signs that China was reclaiming land on disputed South China Sea reefs but stressed it would not be provoked into a rash response.

President Benigno Aquino's spokeswoman Abigail Valte said the government was looking into reports that the Chinese were damaging the reefs in an alleged effort to turn two remote outcrops in the sea into islands.

But she added that Manila would continue to pursue a diplomatic solution to the dispute.

"We do not respond to provocative action, especially (through) military action... we always exhaust the diplomatic channels, as well as other legal means that can help us address this particular issue."

She also reiterated Aquino's earlier remarks that Chinese ships had been spotted in the South China Sea, possibly carrying land reclamation equipment.

The two reefs are within the Spratly Islands region, a disputed archipelago of reefs, islands and atolls in the South China Sea that is coveted by the Philippines, Vietnam, China, Malaysia, Brunei and Taiwan.

Photographs allegedly taken by the Philippine military showing Chinese ships engaged in land reclamation off a reef, were published by the Philippine Daily Inquirer, a major Manila daily on Saturday.

However an Armed Forces spokesman could not confirm if the photos were genuine.

Last month, the Philippines publicly accused Beijing of large-scale reclamation activity at another location within the Spratlys, the Chinese-held Johnson South Reef.

Manila, which also claims the reef, said the reclamation work could lead to China building its first airstrip in the disputed region.

Johnson South Reef lies about 300 kilometers from the large Philippine island of Palawan and is considerably further away from the Chinese coastline.

The Philippines filed a diplomatic protest against China's reclamation works on the reef but Beijing rejected it on grounds the reef is part of Chinese territory.

Tensions have risen over China's claim to most of the South China Sea with the Philippines and Vietnam being the most vocal in recent years in accusing China of using bullying tactics to enforce its claim. With Agence France-Presse