The long-simmering disputes are one issue where the two major powers' influence, focus and military might have been gauged, with the US and China both calling for a peaceful resolution but taking contrasting positions in most other aspects of the conflict.
"Of course, the claimant countries have to answer as a group or individually, and not one country can just give an instant reply because mediation involves all of the claimants and non-claimants", he pointed out.
With China's controversial military buildup likely to be a major issue at the ASEAN summit, Premier Li Keqiang today clearly reiterated Beijing's long- held position that it wants to bilaterally resolve its disputes with its neighbours over the South China Sea.
The two sides are expected to try and expand their economic relations, but it comes at a time of heightened bilateral tensions over territorial disputes in the South China Sea.
"If I can help mediate or arbitrate, please let me know", Trump said in comments at a meeting in Hanoi with Vietnam's president, Tran Dai Quang.
Trump is expected to try during the summit to shore up relations, which have been strained by the mercurial Duterte's notorious anti-US sentiment and his enthusiasm for better ties with Russian Federation and China. Brunei, Malaysia, the Philippines and Taiwan also have claims in the sea. Leaders from China, the United States and seven other nations are joining ASEAN at its annual summit.
"Important that we cooperate to maintain peace, stability, freedom of navigation in and over-flight above the SCS (South China Sea), in accordance with worldwide law".
China has been urged by both South Korea and the United States to take a more active role in curbing North Korea's nuclear and missile ambitions. On Sunday, Philippine President Rodrigo Duterte suggested that, despite their differences, the leaders should not discuss the South China Sea.
Leaders from across Asia joined U.S. President Donald Trump at an extravagant gala dinner in the Philippines' capital on Sunday, a show of amity in a region fraught with tensions that have lurked behind his marathon tour of the continent. "The other hotheads would like us to confront China and the rest of the world on so many issues", Duterte said at a business conference. "The South China Sea, Taiwan, the East China Sea. It can ill-afford a violent confrontation".
Ahead of the next regional meetings, the ASEAN summit in Manila, Chinese state media reported that Xi pledged to work with China's ASEAN partners "to maintain peace and stability, as well as development and prosperity".
Duterte - sometimes described as the "Trump of the East" because of his brash style - said last week he would tell the US president to "lay off" if he raised the issue of human rights when they met.
China's Xinhua news agency said China and Vietnam had agreed to properly handle maritime issues and strive to maintain peace and stability.