China's activity has in particular raised alarm in the Philippines and in Vietnam, where a dispute over an offshore drilling rig sparked deadly anti-Chinese riots last week.
China and the 10-member Association of South East Asian Nations (ASEAN) signed an agreement in 2002 to refrain from occupying uninhabited reefs and shoals in the sea, and from building new structures that would complicate disputes.
"In our view, what they are doing there now is in violation of what we had agreed in the Declaration of Conduct of Parties in the South China Sea," Aquino told reporters.
"The problem is this code is not binding, not enforceable, so we need to come up with a formal code of conduct to resolve the dispute and prevent any potential conflict."
Last week, the Philippine foreign ministry released surveillance photographs of China's reclamation work in Johnson South (Gac Ma) Reef in the disputed Spratly Islands. China appears to be building an airstrip, its first in the Spratlys.
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