Southeast Asian heads of government were due to hold talks on Saturday with visiting global leaders, including US President Joe Biden, as the region tries to navigate the growing rivalry between China and Western powers.
Cambodia is hosting the Association of Southeast Asian Nations (ASEAN) annual summit and a parallel East Asian Summit, with the regional bloc engaging a host of leaders.
Biden, Japanese Prime Minister Fumio Kishida and Australian Prime Minister Anthony Albanese are among the leaders set to hold separate talks with the bloc on Saturday.
Chinese Premier Li Keqiang and South Korean President Yoon Suk-Yeol met ASEAN leaders on Friday.
The US president will focus on the Indo-Pacific region and talk about US commitment to a rules-based international order in the South China Sea in his discussions, senior administration officials said earlier this week.
Some analysts played down expectations of any dramatic developments from Biden's presence at the ASEAN meetings but noted that it provided more evidence of how the United States was returning to "normal diplomacy".
"President Trump didn't attend a single East Asian Summit during four years in office," said Greg Poling, head of the Southeast Asia programme at Washington's Center for Strategic and International Studies.
One outcome of the trip would be the elevation of the US-ASEAN partnership to a comprehensive strategic partnership, he noted.
"That doesn't mean anything concrete, but symbolically it puts the US at the same level as China," said Poling.
Russian Foreign Minister Sergei Lavrov will also attend some meetings, while Ukraine's Foreign Minister Dmytro Kuleba is also in Cambodia after signing a Treaty of Amity and Cooperation with ASEAN as Kyiv seeks to strengthen ties with the bloc.
Kuleba said he held direct talks with several leaders of ASEAN countries, during which he urged them to condemn Russia's invasion of Ukraine, warning that staying neutral was not in their interests.
He said he also urged them to prevent Russia from holding up the movement of Ukrainian agricultural products under a Black Sea grain deal, which could expire on November 19.
The United Nations says 10 million tonnes of grain and other foods have been exported from Ukraine under the arrangement made in July but warns the war will leave millions more hungry.
"I call on all ASEAN members to take every method possible to stop Russia from playing hunger games with the world," Kuleba said at a news conference.
Officials expect a series of regional summits over the next seven days to be difficult, with discussions also expected to include the war in Ukraine, climate and regional tensions over the South China Sea.
G20 leaders are meeting in Bali next week, and the Asia-Pacific Economic Cooperation (APEC) forum will take place in Bangkok after that.
ASEAN leaders on Friday issued a "warning" to Myanmar to make measurable progress on a peace plan or risk being barred from the bloc's meetings as social and political chaos escalates in the country.