Philippine President Rodrigo Duterte will host world leaders in Manila from Sunday, hoping their presence will quieten worldwide criticism over his deadly drugs war, which rights groups say may be a crime against humanity.
US President Donald Trump has offered his services as a "mediator and arbitrator" over disputed territorial claims South China Sea issue, one of the most pressing issues for many of Asia's leaders.
Trump's Asian tour comes as the U.S. rallies for tougher sanctions against North Korea's nuclear program and ballistic missile tests.
The United States has criticized China's construction of islands and its build-up of military facilities in the sea, and is concerned they could be used to restrict free nautical movement.
US President Donald Trump will be among leaders from 19 countries, plus the heads of the United Nations and European Union, coming for the talks, which will begin with a banquet on Sunday night followed by summits on Monday and Tuesday.
Amy Searight, senior adviser of the Southeast Asia Program at the Center for Strategic and International Studies, told reporters before the trip that she expects Duterte to roll out the red carpet for Trump because he "sees this as an opportunity to somewhat reset US-Philippine relations".
Carrying placards declaring "Dump Trump" and "Down with U.S. Imperialism", the left-wing protesters were blocked by police in riot gear with shields and batons, and then showered with jets of water from a fire engine.
In Vietnam on Thursday on the sidelines of an Asia-Pacific economic summit, Duterte boasted that when he was 16 he stabbed to death someone for looking at him the wrong way. "The South China Sea, Taiwan, the East China Sea".
Pacific Rim nation leaders agreed in Vietnam on Saturday to address "unfair trade practices" and "market distorting subsidies", a statement that bore the imprint of Trump's efforts to reshape the global trade landscape.
Ahead of the annual summit of the ASEAN, an influential grouping of 10 South East Asian countries, a number of diplomats said the thorny issue of China's aggressive military buildup in the South China Sea may be one of the focus areas of the deliberations on Tuesday. The country claims a huge swathe of the South China Sea.
Tensions in the contested waters have ratcheted up since 2014 as China has turned sandbars into islands, equipping them with airfields, ports and weapons systems and warned USA warships and aircraft to stay away from them.
Others who will be in Manila for the summit meetings include Chinese Premier Li Keqiang, Russian Prime Minister Dmitry Medvedev and leaders from Japan, Canada, South Korea, India, Australia and New Zealand.