MANILA (AFP) - Philippine President Benigno Aquino on Monday accused China of violating the "Declaration of Conduct" it signed in 2002, after it allegedly began reclaiming land on a disputed reef in the South China Sea.

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.

He stressed that China, along with members of the Association of Southeast Asian Nations (Asean) signed the declaration in 2002 in a bid to ease tensions over the South China Sea, but this agreement was not binding. Mr 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 spokesman Hua Chunying would not confirm Manila's claim over the Johnson South Reef activity, but asserted the outcrop was Chinese territory.

Mr Aquino said the problem was that the Declaration was non-binding, adding that the incident showed the need for a binding "Code of Conduct that would stop these actions that have a potential of causing violence and unrest".

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. The Philippines also filed a separate diplomatic protest against China's reclamation works on Johnson South Reef last month, but Beijing also rejected it on grounds the reef is part of Chinese territory.

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.