Weeks after China threatened to attack Vietnam over oil and gas drilling in the flash point waters, Vietnam insisted that ASEAN foreign ministers meeting in Manila refer to China's build-up and arming of islands in a customary joint communique.

But the ministers delayed releasing one after their annual meeting on Saturday failed to reach a consensus, reflecting the concerns of some countries worried about upsetting Beijing given its growing military and economic influence across the region.

The failure of the ASEAN states to take a joint position comes at a time of uncertainty over how the Trump administration plans to check China's militarisation of the strategic waterways.

he ministers did agree, however, to take tougher response against North Korea's ballistic missile and nuclear program, issuing a statement expressing "grave concern" about Pyongyang's behaviour.

North Korea's top diplomat Ri Yong-ho is in in Manila for broader talks at the 27-member ASEAN Regional forum on Monday.

Australian Foreign Minister Julie Bishop said last week she would push for a widening of sanctions against North Korea at what has become Asia's biggest security forum.

US Secretary of State Rex Tillerson also wants ASEAN states to further increase diplomatic pressure on Pyongyang.

The United Nations Security Council on Saturday unanimously adopted a resolution to impose punishing sanctions on North Korea that analysts said could reduce the secretive state's annual export revenue by $US1 billion ($1.2 billion).

The US painstakingly negotiated the sanctions with China, a long-time ally of North Korea and its most important trading partner.

Analysts say the ASEAN foreign minister's failure to reach consensus on the South China Sea highlights the impotence of the regional grouping on the most critical issue facing their region.

The ministers only agreed to endorse a "framework" of a code of conduct (COC) on the South China Sea that has been negotiated for a decade.

The COC is not legally binding for the ASEAN states and refers only to "mutual trust, co-operation and confidence" in the way they handle disputes in the South China Sea, almost all of which is claimed by China.

The Philippines, Malaysia, Vietnam, Taiwan and Brunei have overlapping claims in strategically vital and resource-rich waterways.

Vietnam responded to China's threat to attack its bases in July by ordering a shutdown of drilling in an area about 400 kilometres off Vietnam's coast.

Carl Thayer, an expert on Vietnam and the South China Sea from the Australian Defence Force Academy, said at the time that China's threats "are an alarming escalation of Chinese assertiveness and forms part of an emerging pattern of increased Chinese bellicosity."

By Lindsay Murdoch - The Sydney Morning Herald - August 6 2017