Animosity over China's competing territorial claims with several neighbours is dominating meetings of the Association of Southeast Asian Nations ( ASEAN), which began in Myanmar's capital Naypyidaw on Friday and are broadening to include key world powers ahead of security discussions on Sunday.
The United States has waded into the row, calling for an end to all "provocative" acts in the South China Sea, a crucial maritime route that is also believed to hold huge oil and gas deposits.
US Secretary of State John Kerry, who arrived in the early hours Saturday to attend a series of meetings with regional and international powers, is expected to underline the message during his visit.
ASEAN foreign ministers have expressed concern over tensions in the disputed areas of the South China Sea.
"I asked everyone to see that the situation was getting to a point where it would no doubt begin to affect the peace, security and stability of the region," said Philippine Foreign Secretary Albert del Rosario late Friday.
He said he had urged the regional bloc to call for "a cessation of all activities that escalate tension" in accordance with the existing ASEAN and Chinese framework to deal with disputes in the contested waters.
Beijing claims sovereignty over almost the entire sea, including waters, islands, reefs, shoals and rocky outcrops nearer to other countries.
ASEAN states Brunei, Malaysia, the Philippines and Vietnam are claiming parts of the sea, while Taiwan is a sixth claimant.
Ties between China and Vietnam sunk to their lowest point in decades in May after Beijing moved a deep-sea oil rig into disputed waters near the Paracel Islands, triggering deadly anti-China riots in Vietnam.
Beijing has since removed the rig, in a move that analysts say was aimed at deflecting accusations of aggressive maritime behaviour.
A draft statement from ASEAN foreign ministers, who met Friday, said the 10-member bloc had "serious concern" over recent developments in the disputed sea.
It also called for an end to "destabilising actions". That wording is likely to have proved contentious for China's supporters in ASEAN and no final statement had been released by early Saturday.
The Philippines has been at the forefront of protest against China and has challenged Beijing's claims before a UN tribunal.
It has also protested Chinese reclamation works in disputed reefs, including a suspected airstrip.
In March, China tried to block a resupplying mission by Manila to a shoal in the Spratlys, after also seizing another South China Sea shoal from the Philippines in 2012.
Manila wants a speedy conclusion of talks for a legally binding code of conduct, and the establishment of a dispute settlement mechanism anchored in international law.
Foreign Secretary del Rosario said he had received support for his proposals but said they would be referred to senior officials for further consideration.
The maritime row is set to loom large over discussions at the ASEAN Regional Forum on Sunday.
The forum is an annual security dialogue among foreign ministers of the 10-member ASEAN and key partners, including Australia, China, India, Japan, South Korea, Russia and the European Union.