MANILA - Vietnam urged other Southeast Asian nations to take a stronger stand against Chinese expansionism in the South China Sea as a tense regional security forum began Saturday with North Korea also under fire over its nuclear programme.

Ahead of the launch of the annual gathering of foreign ministers from the 10-member Association of Southeast Asian Nations (ASEAN), Vietnam made a bold play against China with a raft of suggested changes to a planned joint communique.

It set the stage for what was expected to be a fiery few days of diplomacy in the Philippine capital, with the top diplomats from China, the United States, Russia and North Korea set to join their ASEAN and other Asia-Pacific counterparts for security talks from Sunday.

The meetings will take place as the United Nations Security Council votes this weekend on a US-drafted resolution to toughen sanctions against North Korea to punish the isolated regime for its missile and nuclear tests.

The United States said it would also seek to build united pressure on the North at the Manila event -- known as the ASEAN Regional Forum -- and Philippine Foreign Secretary Alan Peter Cayetano said Pyongyang would receive a strong message.

But on the South China Sea dispute -- one of Asia's other top powder keg issues -- there was far less consensus, with Vietnam resisting efforts by the Philippines to placate Beijing, diplomats told AFP.

Vietnam on Friday night sought to insert tough language against China in an ASEAN statement that was scheduled to be released after the Southeast Asian ministers wrapped up their own talks on Saturday.

According to a copy of a draft obtained by AFP, Vietnam lobbied for ASEAN to express serious concern over "construction" in the sea, in reference to China's explosion of island-building in the disputed waters in recent years.

Vietnam also wanted ASEAN to insist in the statement that a planned code of conduct for the sea with China be "legally binding", which Beijing opposes.

TENSE TALKS

The lobbying occurred when the ASEAN foreign ministers held unscheduled and informal talks late on Friday night.

"The discussions were really hard. Vietnam is on its own to have stronger language on the South China Sea. Cambodia and Philippines are not keen to reflect that," one diplomat involved in the talks told AFP.

China claims nearly all of the strategically vital sea, including waters approaching the coasts of Vietnam, the Philippines, Malaysia and Brunei.

China has in recent years expanded its presence in the sea by building the artificial islands, which are capable of holding military bases.

Alongside Vietnam, the Philippines used to be the most vocal critic of Beijing's expansionism.

But under President Rodrigo Duterte, Manila has sought to downplay the dispute with China in return for billions of dollars in Chinese investments and aid.

China has in recent years also successfully lobbied other ASEAN nations, particularly Cambodia and Laos, to support its diplomatic maneuvering in the dispute.

At the ASEAN opening ceremony on Saturday morning, Cayetano confirmed there had been strong debates on Friday.

"You have to excuse my voice as my colleagues, we kept each other up until almost midnight last night. In the true ASEAN way, we were able to passionately argue our national interest," Cayetano said.

Various diplomats said that Vietnam was likely to lose its battle to insert the strong language against China, with the Philippines as host of the talks wielding greater influence.

ASEAN is set to this weekend endorse a framework for a code of conduct with China, which is meant to pave the way for more concrete action.

But security analysts point out that the framework comes 15 years after negotiations on the issue first began, and China has used that time to cement its claims with the artificial islands.

Another pressing issue in Manila will be the growing terrorism threat in the region.

The event is taking place as Philippine security forces battle Islamic State-aligned gunmen who have since May been occupying parts of Marawi, the nation's main Muslim city about 800 kilometers south of Manila.