Southeast Asian leaders on Sunday pressed their call for self-restraint in the disputed South China Sea and renewed their alarm over the US-China trade war, with one leader warning it may spiral out of control.

The long-raging territorial conflicts and the protracted dispute between the two global economic powerhouses are high on the agenda in the final of two days of meetings of leaders from the Association of Southeast Asian Nations. It's an annual summit steeped in diplomacy, protocol and cultural color in the Thai capital.

Facing regional predicaments such as the Rohingya refugee crisis in Myanmar, the leaders took the stage and clasped their hands together in a trademark ASEAN handshake to project unity.

Founded in 1967 in Bangkok in the Cold War era, the diverse 10-nation bloc lumps together an absolute monarchy and constitutional monarchies, along with socialist republics and fledgling democracies.

This year's host, Thai Prime Minister Prayuth Chan-ocha, opened the summit with a call for regional unity and a push for the bloc to conclude a massive free trade pact with China and five other Asia-Pacific nations to cushion any impact from America's trade conflicts with China.

"The winds of protectionism that are battering the multilateral system remind us that we must hang on ever stronger to one another," Prayuth said.

The US, which has pursued bilateral deals over multination trade accords under President Donald Trump, is not included in the Regional Comprehensive Economic Partnership, or RCEP, which Prayuth said would encompass the world's largest free-trade region.

Officials from Singapore, Thailand, Indonesia and Vietnam will be at the G-20 summit later this month in Japan, where Trump and Chinese President Xi Jinping are expected to meet, and express the region's concerns.

"ASEAN hopes there will be discussions that lead to an easing and resolution of these problems because they affect many countries," Prayuth said.

Philippine President Rodrigo Duterte told other leaders on Saturday that the trade conflict between Washington and Beijing "is creating uncertainty. It is taking a toll on global growth and it could hinder the ongoing processes of economic integration."

"The US and China must both take the high road and resolve their differences before the situation spirals out of control," the usually blunt Duterte said.

In their public communiques, the leaders have avoided naming the US and China or specific nations embroiled in controversial issues in a show of their conservative protocols. The leaders, however, could raise thorny issues in a closed-door and informal session.

Duterte has said he would raise the territorial conflicts in the South China Sea following the June 9 ramming of an anchored Philippine boat by a larger Chinese fishing vessel in the disputed Reed Bank. The incident sparked an outcry and condemnations in the Philippines after the Chinese crew sailed away while the fishing boat sank at night. Its Filipino crew was rescued by a Vietnamese vessel.

Known for his close ties with China, Duterte has backed Beijing's initial assertion that the collision was accidental. He mocked calls for him to immediately take drastic actions and agreed to a joint investigation with China, which critics have opposed.

In a statement outlining their regional policies, the leaders on Sunday renewed their call for countries involved in the territorial spats to "exercise self-restraint in the conduct of activities and avoid actions that may further complicate the situation, and pursue the peaceful resolution of disputes in accordance with international law."

Four ASEAN states — the Philippines, Vietnam, Malaysia and Brunei — along with Taiwan and China are locked in disputes over the strategic waterway. ASEAN has been in talks with China to negotiate a nonaggression pact called the "code of conduct" to prevent major armed clashes in the offshore region, which has long been regarded as a potential Asian flashpoint.

Southeast Asian diplomats have told The Associated Press that the first of three rounds of talks on the proposed pact was expected to be completed this year. The more difficult aspects, including whether the pact should be legally binding and cover the entire disputed region, have been relegated to the final rounds so as not to stall the talks early on.

While China has praised the negotiations as a show of Asian nations' ability to manage their conflicts peacefully, critics doubt if such a code of behavior can make a difference given Beijing's increasingly aggressive assertion of its claims in the strategic waters.

They cite China's construction of islands on seven disputed reefs in recent years despite it being a party to a 2002 non-binding regional agreement discouraging such actions.

China initially claimed some of the islands would serve as storm shelters for fishermen but Beijing instead installed defensive missile systems there and its naval forces shoo away and warn ships and aircraft that stray near.