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.
Persons:
Ferdinand Marcos, Jr, Lee Hsien Loong, Ministry of Foreign Affairs Sarun, Pham Minh Chinh, Fumio, Yoon Suk Yeol, Joko, Kamala Harris, Li Qiang, Sergei Lavrov, China's Li, Harris, Joe Biden, Fumio Kishida, Kanupriya Kapoor, Robert Birsel
Organizations:
Singapore's, Ministry of Foreign Affairs, Vietnam's, Japan's, ASEAN, Russian, Association of Southeast Asian Nations, White, U.S, Japanese, Thomson
Locations:
Philippines, Fumio Kishida, South, JAKARTA, Indonesia, Japan, South Korea, India, Australia, South China, Myanmar, Korea, Russia, United States, Southeast Asia, China, Laos