President Donald Trump has offered to mediate in the South China Sea disputes, while his Chinese counterpart played down concerns over Beijing's military build-up and the prospects of war in the contested waters.
Chinese President Xi Jinping met with Vietnamese Communist Party chief Nguyen Phu Trong during a state visit to Hanoi on Sunday, after Trump also visited the country.
China's Xinhua news agency said China and Vietnam had agreed to properly handle maritime issues and strive to maintain peace and stability.
The remarks were made when Xi held talks with Vietnamese President Tran Dai Quang in Hanoi during a state visit to the Southeast Asian country.
Reefs and islands in the South China Sea are disputed by Brunei, Indonesia, Malaysia, the Philippines and Taiwan, as well as China and Vietnam.
According to the new "Declaration for a Decade of Coastal and Marine Environmental Protection in the South China Sea (2017-2027)", the leaders note that "the current environmental situation in the South China Sea requires collective attention and action to protect the marine ecosystem and biodiversity".
China has in recent years built artificial islands and airstrips capable of hosting military installations in contested areas to cement its claims, inflaming tensions with its neighbours.
Mr Trump's offer faces major obstacles, as China has steadfastly opposed what it calls USA meddling in the disputes and is unhappy about the USA navy's incursions into what Beijing considers its territorial waters in the South China Sea.
"If you go to the negotiating table and you start with the statement that I am here to claim validity of our ownership, you're wasting your time".
"It is a very kind, generous offer because he is a good mediator".
"China's greatest hope is for peace and stability in the South China Sea", Li told ASEAN leaders in Manila.
However no timeframe was announced for an actual code.
Signing China up to a legally binding and enforceable code for the strategic waterway has always been a goal for claimant members of ASEAN, some of which have sparred for years over what they see as China's disregard for their sovereign rights and its blocking of fishermen and energy exploration efforts.
Xi spoke about the territorial rifts ahead of the ASEAN summit in the Philippines, which also includes the U.S., China and other global players.
The Philippines had for many years stood alongside Vietnam as one of the region's strongest opponents to Chinese expansionism.
Philippine President Rodrigo Duterte said Xi, during a meeting in Danang, Vietnam, where they attended the annual Asia-Pacific Economic Cooperation forum last week, assured him of China's peaceful intentions in the strategic waterway, where Beijing, the Philippines, Vietnam and three other governments have overlapping claims.