As foreign ministers met in the Cambodian capital Phnom Penh, Prime Minister Hun Sen said hammering out a code of conduct with China in the disputed waters was a chief goal for the 10-member Association of Southeast Asian Nations (ASEAN).
Tension over competing claims in the South China Sea promises to be the hot button issue of the meetings, particularly later in the week when US Secretary of State Hillary Clinton and her Chinese counterpart are among regional participants for the security-focused ASEAN Regional Forum (ARF).
In his opening address Hun Sen urged delegates to "give emphasis" to working towards a code of conduct in the sea, which will provide guidelines to resolving disputes over a web of conflicting territorial claims involving several member nations.
He said ASEAN should show that it can be a "driving force for the promotion of dialogue and cooperation" on political and security issues.
"Maintaining regional peace and security is indispensable for ASEAN prosperity," said the Cambodian leader, whose country currently holds the rotating chairmanship of the bloc.
Tensions have risen recently in the sea, with both Vietnam and the Philippines accusing Beijing of aggressive behaviour.
Manila is leading a push for ASEAN to unite to persuade China to accept a code of conduct but Beijing has preferred an approach that would deal with the claimants individually.
Senior diplomats attending the meetings in Cambodia said ASEAN was still wrangling over how to approach the issue without offending China, the world's second biggest economy and a major trade partner for many Southeast Asian states.
One diplomat, who asked not to be named, said ASEAN has yet to reach consensus on whether to mention the recent standoff between Chinese and Philippine ships in the disputed Scarborough Shoal in a joint communique.
Another statement, to be issued at the end of the wider ARF meeting, is expected to refer to the South China Sea issue in general terms, another diplomat said.
China claims essentially all of the South China Sea, home to vital shipping lanes and believed to be rich in oil and gas deposits. Taiwan and ASEAN members the Philippines, Vietnam, Brunei and Malaysia also have claims in the waters.
China recently angered Vietnam by inviting bids for exploration of oil blocks in contested waters, sparking protests in Hanoi.
US Secretary of State Clinton on Sunday urged "progress" on the code of conduct in the sea.
The strategic rivalry between Washington and Beijing is expected to loom large over the summit, following the recent expansion of US military relations with the Philippines and Vietnam.
But observers predict Clinton will be eager to downplay any friction with China and may be less outspoken on the maritime dispute than in the past.
ASEAN comprises Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam -- a grouping of nearly 600 million people from disparate economic and political systems.
The bloc has often been dismissed as a talking shop but it has assumed new strategic importance in light of Washington's foreign policy "pivot" to Asia and the economic rise of China in recent years.