World leaders were on Thursday set for a series of meetings on security and trade against a backdrop of simmering tensions and open conflicts in parts of the world, as an ASEAN-hosted summit in Indonesia entered its final day.

US Vice President Kamala Harris, Chinese Premier Li Qiang, and Russian Foreign Minister Sergei Lavrov are attending the summit led by the Association of Southeast Asian Nations (ASEAN), along with leaders of partner countries Japan, South Korea, India, Australia and others.

An undercurrent of tension has accompanied the talks on issues from trade and technology to China's increasing assertiveness in the South China Sea, the Myanmar junta's refusal to cooperate with ASEAN on a peace plan, and suspicion North Korea plans to supply weapons to Russia.

On Wednesday, China's Li warned against starting a "new Cold War" and warned countries against taking sides in any conflict.

Harris, attending the meetings instead of President Joe Biden, reiterated a U.S. commitment to the region.

"The United States has an enduring commitment to Southeast Asia and more broadly to the Indo-Pacific," she said.

A White House official said earlier the U.S. shared interests with ASEAN in "upholding the rules-based international order, including in the South China Sea, in the face of China's unlawful maritime claims and provocative actions".

The Chinese premier and Japanese Prime Minister Fumio Kishida met briefly on the sidelines of the summit on Wednesday and discussed Japan's release into the sea of treated radioactive water from the Fukushima nuclear plant.

An infuriated China has banned on all aquatic imports from Japan in response. It was not clear if the two would hold a bilateral meeting on Thursday.

Indonesia, chair of the 10-member ASEAN, is expected to symbolically hand over the chair to Laos on Thursday, though it will maintain the role until the end of the year.