I am a very good mediator, " the deal-making American leader told Vietnamese President Tran Dai Quang during an official state visit.
Trump was in Manila on Monday for meetings with the 10-member Association of Southeast Asian Nations (ASEAN) and several other countries. "He knows that if he goes to war, everything will blow up".
President Quang said Vietnam believed in handling disputes on the South China Sea through peaceful negotiations and on the basis of worldwide laws - which Vietnam says nullify China's claims.
Duterte has grown closer to China since he took office past year and Vietnam has emerged as Beijing's main challenger in the area.
In addition to claiming the vast majority of the 1.4 million square miles (3.5 million square kilometers) of sea - China has built-up small islands in the sea and outfitted them with missile systems, much to the chagrin of its Asian neighbors and the United States.
Citing a source with firsthand knowledge of the investigation, ESPN reported the players could be in Hangzhou for "a week or two" while the situation is resolved.
The two parties said it "is important that we cooperate to maintain peace, stability, freedom of navigation in and overflight above the SCS, in accordance with worldwide law", including the 1982 United Nations Convention on the Law of the Sea (UNCLOS).
A report from the Associated Press said Southeast Asian leaders were to announce Monday the start of negotiations with China on a so-called "Code of Conduct" in the disputed South China Sea in what they regard as a milestone but some experts dismiss as a non-starter.
The Asean summit opens on Monday under extra-tight security at a theatre and convention complex by Manila Bay.
Vietnamese and USA companies signed memorandums of understanding on gas development and automobiles as well as aircraft engine purchase and support during Trump's visit.
"I assure you that the relations between the two countries are strong, as always been, no problem for that".
Xi and US President Donald Trump, among others, just finished an Asia-Pacific economic summit in the Vietnamese coastal city of Da Nang.
"We're also concerned about what's happening in the South China Sea - the continued buildup of military installations, and in our bilateral last night with Mr. Xi Jinping, I told the President our misgivings", Duterte told Turnbull.
Contempt for China runs deep in Vietnam, a country that was colonized by China for almost 1,000 years.
The Philippines had for many years stood alongside Vietnam as one of the region's strongest opponents to Chinese expansionism.