At the summit, which opened Monday, the leaders from the 10 ASEAN member states will discuss regional cooperation and developments.
Also in Manila are leaders of ASEAN’s dialog partners, including the US, China, Japan, South Korea, Russia, Australia and India.
The annual gathering opened amid fresh clashes between Philippine security forces and the protesters angry at a visit by US President Donald Trump to Manila.
Hundreds of protesters marched on the summit’s venue near Manila Bay. The rally turned violent when riot police intervened, using water cannons and blocking the demonstrators.
Trump, who arrived in Manila Sunday on the last leg of his trip to Asia, angered people who fear he may want more military bases in the Philippines and drag their country into a possible conflict with North Korea.
During the summit, a range of regional issues will be discussed, including the Rohingya crisis in Myanmar, the North Korean military program, the spread of extremism in the region, and the territorial dispute in South China Sea.
On the sidelines of the Monday event, US president sat down for talks with his Philippine counterpart, Rodrigo Duterte.
He also met with prime ministers of Australia and Japan, namely Malcolm Turnbull and Shinzo Abe, with their talks focusing on North Korea’s military program as well as trade ties.
Trump said “a lot” of progress had been made in negotiations on trade with the two leaders.
In a briefing to media, Turnbull accused North Korea of “recklessness,” saying Pyongyang needs to be stopped.
Abe also said that their most immediate challenge was to ensure regional peace and stability.
According to a draft of a statement to be issued during a summit meeting in Manila on Monday, Southeast Asian countries agree that the relative calm in the territorial dispute over the South China Sea should not be taken for granted.
“While the situation is calmer now, we cannot take the current progress for granted,” said the draft, a copy of which was seen by Reuters.
“Important that we cooperate to maintain peace, stability, freedom of navigation in and over-flight above the SCS (South China Sea), in accordance with international law,” it said.
The statement which will be issued after a meeting between China and the 10-member ASEAN bloc adds, “It is in our collective interest to avoid miscalculations that could lead to escalation of tensions.”
The South China Sea has been the subject of a territorial dispute between China and Vietnam, Taiwan, the Philippines, Malaysia, and Brunei. But those countries seem to have been managing their disputes with China smoothly.
Chinese President Xi Jinping, who met Duterte last week in Vietnam, said his government guarantees “safe passage” for all countries using the South China Sea.
Trump also stepped in and offered to help settle the maritime dispute saying, "If I can help mediate or arbitrate, please let me know."
China, however, called for him to stay away from the territorial dispute, saying, “The South China Sea issue isn’t an issue between China and the United.
On Tuesday, ASEAN will have a 40th anniversary commemorative summit with the European Union. It will be followed by the East Asia Summit (EAS), which is composed of ASEAN members, Australia, China, India, Japan, New Zealand, Russia, South Korea and the United States.