North Korea's defiant missile testing and the South China Sea territorial row were among a barrage of security threats in focus Thursday as US President Barack Obama gathered with East Asian leaders in Laos.

The annual event this year comes at a time of heightened tensions on a wide range of fronts across the region, with terrorism also a concern after deadly bomb blasts in Thailand and the Philippines in recent weeks.

Obama was due to meet on Thursday morning with the leaders of the 10-member Association of Southeast Asian Nations (ASEAN) bloc, pitting him against firebrand Filipino leader Rodrigo Duterte who this week branded him a "son of a whore".

The expanded East Asia summit will then take place, which involves members of the long-running and increasingly fraught six-nation talks aimed at convincing North Korea to give up its nuclear ambitions.

Defying the international community and UN sanctions, North Korea on Monday conducted the latest in a series of ballistic missile tests that have rattled nerves across the region.

Obama warned on Monday shortly after arriving in Laos that Kim Jong-Un's regime was dooming itself to further isolation, and the UN Security Council condemned the tests.

But North Korea responded in typically bellicose fashion, threatening on Wednesday to take "further significant measures".

- 'Serious concern' -
The 18 East Asia summit nations will voice "serious concern" over the latest North Korean tests, according to a draft of their end-of-meeting statement obtained by AFP.

"We reaffirmed the importance of peace and security in this region and reiterated support for the denuclearisation of the Korean Peninsula in a peaceful manner," the statement said.

The statement will also emphasise the importance of maintaining peace in the South China Sea, the other major regional flashpoint.

China came under pressure at ASEAN's standalone summit on Tuesday and Wednesday over its land reclamation efforts in the sea, which are aimed at cementing control over the strategically vital waters.

An international tribunal ruled in July that Beijing's claims to nearly all of the sea had no legal basis, and its artificial island-building activities were illegal.

- Muted statement expected -
China insists it has sovereign rights to most of the sea -- through which $5 trillion in global shipping trade passes annually -- even waters close to Southeast Asian nations.

But it has vowed to ignore the ruling and the Philippines released photos on Wednesday claiming to show that Beijing was continuing with its island-building campaign.

Chinese Premier Li Keqiang has been in Laos this week and faced questioning over the issue, with ASEAN leaders voicing alarm.

"We remain seriously concerned over recent and ongoing developments and took note of the concerns expressed by some leaders on the land reclamations," said a joint statement at the end of their summit on Wednesday.

Nevertheless, intensive Chinese lobbying helped to ensure there was no mention of the July ruling in the ASEAN statement.

The East Asia bloc was expected to urge all parties to follow international law, but otherwise release a muted statement on the South China Sea.

"We reaffirmed the importance of maintaining peace, stability, security and freedom of navigation in and over-flight in the South China Sea," the draft of its post-summit statement said.

A spectacular sideshow to this week's diplomacy in Laos has been the spat between the acid-tongued Duterte and Obama, leaders of nations that have been longtime allies.

Duterte launched a barrage of insults against Obama after being told the US president planned to raise concerns about a war on crime in the Philippines that has claimed 3,000 lives in just over two months.

"You must be respectful. Do not just throw away questions and statements. Son of a whore, I will curse you in that forum," Duterte told reporters.

Obama cancelled a meeting with Duterte scheduled for Tuesday because of the outburst.

They met briefly on Wednesday night before a leaders' dinner, but only exchanged "pleasantries", according to the White House.