NAYPYIDAW, Myanmar - Southeast Asian leaders met Sunday for a historic summit in former pariah Myanmar overshadowed by soaring tensions in the South China Sea and growing fears over Beijing's territorial assertions.
The 10-member Association of Southeast Asian Nations ( ASEAN) is convening just days after both Vietnam and the Philippines locked horns with China in contested waters, stoking international alarm.
The summit, hosted for the first time by Myanmar in its showpiece capital Naypyidaw, is set to be dominated by discussion of the South China Sea, which is crisscrossed by key shipping lanes and thought to contain vast energy reserves.
In his opening address, Myanmar President Thein Sein said "regional and global issues of great concern to ASEAN will be extensively discussed among ourselves", without directly mentioning the escalating maritime crisis.
ASEAN foreign ministers expressed "serious concerns over the on-going developments" in a joint statement released Saturday as the bloc sought to present a unified front in dealing with the region's massive neighbour.
"The South China Sea continues to be a litmus test for ASEAN, but I think ASEAN will not be found wanting," Indonesian Foreign Minister Marty Natalegawa told reporters on Saturday.
Tensions flared this week after Beijing controversially relocated a deep-water oil rig into territory also claimed by Hanoi.
The area around the drilling well has since seen several collisions between Chinese and Vietnamese ships, with the communist neighbours each blaming the other for the rise in tensions.
The stand-off has stoked bitter anti-China sentiment in Vietnam, with about 1,000 people joining one of the country's largest ever rallies against Beijing in Hanoi on Sunday. Protests also broke out in two other major Vietnamese cities.
China and Vietnam, who fought a brief border war in 1979, frequently trade diplomatic barbs over oil exploration, fishing rights and the Spratly and Paracel Islands.
Vietnam's communist regime, which is wary of public gatherings that could threaten its authoritarian rule, has alternated between tolerating anti-China rallies and violently breaking them up.
Exercise 'utmost restraint'
UN Secretary General Ban Ki-moon called on both countries to "exercise the utmost restraint" in the sea, United Nations deputy spokesman Farhan Haq said Friday.
Observers have said Beijing's decision to move the rig could have been a tit-for-tat response to a visit to the region by US President Barack Obama, who reaffirmed support for Asian allies the Philippines and Japan, which is locked in its own maritime territorial dispute with China.
Beijing claims sovereign rights to almost the whole of the South China Sea.
The Philippines and Vietnam are China's most vocal critics within Southeast Asia.
But the South China Sea is also claimed in part by ASEAN members Brunei and Malaysia as well as Taiwan.
Manila, which has asked a UN tribunal to rule on China's claims over most of the sea, also said on Wednesday it had detained a Chinese fishing boat in disputed territory.
Philippine President Benigno Aquino Saturday urged fellow Southeast Asian leaders to face up to the threat posed by China's increasing assertiveness in the sea, stressing that it affected regional security.
Beijing prefers to negotiate directly with its smaller, weaker neighbours on a bilateral basis, a policy that is rejected by rival claimants.
The other ASEAN members are Cambodia, Indonesia, Laos, Myanmar, Singapore and Thailand.
Myanmar's chairmanship is the first time it has taken the helm of ASEAN, despite having been a member for 17 years, as concerns about the rights record of the former junta kept the country on the sidelines.
But reforms under a quasi-civilian regime that came to power in 2011 have burnished the country's international standing and seen the removal of most Western sanctions.
Thailand's contribution to the summit will be overshadowed by the removal of Thai premier Yingluck Shinawatra from office for abuse of power in a recent court ruling that drew both pro- and anti government protesters onto the streets.