Philippine President Rodrigo Duterte failed to condemn China's push to control most of the disputed South China Sea on Sunday after hosting a regional summit, handing Beijing a political victory.

A day after taking centre stage as host of an Association of Southeast Asian Nations leaders' meeting, Duterte released a bland chairman's statement that ignored last year's international ruling outlawing China's sweeping claims to the key waterway.

"We took note of concerns expressed by some leaders over recent developments in the area," said the 25-page statement without any mention of what these issues were, which countries were thought to be responsible, and which heads of state raised them.

China has been turning reefs and shoals in areas of the sea claimed by the Philippines and other nations into artificial islands, and installing military facilities on them.

ASEAN members Vietnam, Malaysia and Brunei also claim parts of the sea, but China insists it has sovereign rights over nearly all of it.

Throughout the summit Duterte said the Philippines and other nations were helpless to stop the island building, so there was no point discussing it at diplomatic events such as Saturday's meeting.

China is not a member of the 10-nation ASEAN, but its ambassador to Manila worked hard to influence the tenor and content of the chairman's statement, diplomats earlier told AFP.

Analysts agreed the bland statement was a result of Chinese pressure.

"This reflects the Cambodianisation of Philippine foreign policy. We're starting to behave like Cambodia, which is extremely sensitive to China's strategic interests," said Renato de Castro, international studies professor at Manila's De La Salle University.

At an ASEAN foreign ministers' meeting last year in Laos, Cambodia -- which has strong economic ties to Beijing -- controversially blocked a proposed joint communique referring to the international tribunal's ruling against China.

Duterte has vowed not to "taunt or flaunt" the tribunal ruling while pushing closer ties with China in the hopes of attracting billions of dollars in Chinese investment.

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His predecessor Benigno Aquino had pushed hard at ASEAN summits for the bloc to voice its strong opposition to Chinese expansionism, and official statements at those events often reflected that.

Aquino also filed the case at the international tribunal. But the ruling against China came after Duterte took power last year.

"On the ground, there is no hindrance to China achieving absolute dominance in the South China Sea, whether in military or civilian terms, regardless of parameters set by international law," said Jay Batongbacal, from the University of the Philippines.

The statement "makes it more difficult for ASEAN to agree soonest on a consistent and unified basis for dealing with China and the maritime disputes," he said.

An earlier draft of the chairman's statement seen by AFP cited a reference to "respect for legal and diplomatic processes".

Another version also contained a call, championed by Vietnam according to diplomats, to cease "land reclamation and militarisation" of the sea.

Both references were absent in Sunday's final statement.