China wants to work with the Association of Southeast Asian Nations (ASEAN) to "dispel interference" in the disputed South China Sea, Premier Li Keqiang said during a regional summit in the Lao capital Vientiane.

The Philippines said on Wednesday it was "gravely concerned" that Chinese boats were preparing to build structures at a disputed shoal in the South China Sea, shattering an appearance of cordiality at the summit.

China claims much of the South China Sea, through which more than $5 trillion of trade moves annually. Vietnam, the Philippines, Malaysia, Brunei and Taiwan also have claims.

Officials said talks between Southeast Asian leaders and Li went smoothly, but there was no reference to a July court ruling in The Hague that declared illegal some of China's artificial islands and invalidated its claims to almost the entire waterway.

In a statement released later on Wednesday by China's Foreign Ministry about the meeting, Li was paraphrased as saying China was willing to work with ASEAN countries in "dispelling interference ... and properly handling the South China Sea issue".

He did not elaborate, but such wording is typically used by Chinese leaders to refer to not allowing countries from outside the region with no direct involvement in the dispute, like the United States, from getting involved.

With joint efforts from China and ASEAN members, the situation in the South China Sea is moving towards a positive direction, Li added.

Peace and stability in the South China Sea was directly related to prosperity and development of countries in the region, he said.

"Countries in the region are the biggest beneficiaries of peace in the South China Sea. History and facts have repeatedly showed that the South China Sea can only be peaceful and stable so long as the regional countries themselves get hold of the key to fixing the problems," Lie said.

Increasingly assertive action by China's coast guard ships in the South China Sea risks destabilising the region, according to the authors of new research tracking maritime law enforcement incidents across the vital trade route.

Hours before the meeting, however, the Philippines' defence ministry released photographs and a map showing what it said was an increased number of Chinese vessels near Scarborough Shoal, which China seized after a standoff in 2012.

Li made no direct mention of Scarborough Shoal in the comments provided by the foreign ministry. (Reporting by Ben Blanchard; Editing by Michael Perry)