Manila last week publicly accused Beijing of large-scale reclamation activity at Johnson South Reef, which is also claimed by the Philippines. Filipino officials fear this could lead to China building its first airstrip in the disputed region.
"In my view... What they are doing now, this is all seemingly in violation of what we agreed in the Declaration on the Conduct of Parties in the South China Sea," he told reporters.
Aquino said the statement effectively called on all parties to refrain from building new structures in the disputed area until the conflict is settled.
China claims almost all of the resource-rich waters, parts of which are also claimed by ASEAN members, the Philippines, Brunei, Malaysia and Vietnam and non-member Taiwan.
Chinese foreign ministry spokeswoman Hua Chunying would not confirm Manila's claim over the Johnson South Reef activity, but asserted the outcrop was Chinese territory.
The dispute over the reef, which the Chinese navy seized from Vietnam in a deadly 1988 skirmish, is among a tangle of maritime rows in the sea involving the Asian superpower and its smaller and weaker neighbours.
The Philippines had asked a United Nations tribunal in March to declare what Manila said was China's claim to 70 per cent of the sea as illegal.
In another area of the sea, China moved an oil rig into waters claimed by Hanoi, sparking a clash between Chinese and Vietnamese vessels earlier this month.
The dispute has triggered the worst anti-Chinese rioting in Vietnam in decades, targeting Chinese and other foreign-owned factories.
