"We assure the nation that his aforementioned absence has nothing to do with his physical health and well-being which have been the subject of speculation".
News website Rappler reported the country's presidential spokesman Salvador Panelo clarifying that Duterte's absence was not due to his health.
"PRRD will also not attend the gala dinner scheduled tonight and will instead rest", the official said.
However, only a short time later at 11:00 a.m., Duterte was nowhere in sight when ASEAN leaders were scheduled to meet with South Korean President Moon Jae-In, reports ABC-CBN.
The president's health has been a constant source of speculation since he disappeared from public view for a week a year ago - and he has said openly that he is exhausted and would like to step down before his presidential term ends in 2022.
Trump's security adviser, John Bolton, told reporters on Tuesday that the ASEAN meetings tended to be relatively flexible and Pence's schedule was still being decided, but that some would be aimed at preparing for a meeting between China's president and Trump at the G-20 meeting in Argentina later this month.
If a sitting president dies, is permanently disabled or removed through impeachment, the vice-president succeeds to serve the remaining years in a six-year, single term.
He is the oldest person ever to be elected president in the Philippines, but he is far from the most veteran world leader attending ASEAN.
While Asean and China continue to negotiate a "code of conduct" in the disputed areas, talks that have been ongoing since 2002, President Donald Trump's administration has made clear through toughened rhetoric and action that it won't accept any final agreement that undermines or infringes on its interests in the area.
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"I'm delighted by this very innovative experimental approach It's an experiment, but a very important first step in my view". Trump was scheduled to visit the Suresnes American Cemetery and Memorial in the suburbs of Paris .
Mr Duterte has cited Ms Robredo's "incompetence" as a reason for his inability to quit as President. The Philippines' term ends in 2021, a year before Duterte is supposed to step down as president.
"Last night, the President worked late and had only less than three hours of sleep", he said.
President Duterte, who is 73 years old, is well-known to be a late riser who starts working in the early afternoon.
China was "already in possession" of the South China Sea, and that military drills by the United States and its allies were creating "frictions" that were derailing efforts to settle rows over these waters between Beijing and its neighbours.
"China is there. That is the reality", he told reporters before joining the morning's meetings.
"I do not mind everybody going to war, except that the Philippines is just beside those islands".
Chinese Premier Li Keqiang said the region has set a good example of managing those territorial disputes and keeping the peace as it works toward setting a "code of conduct" to govern navigation and other activities.
Upon landing at the summit, attended by regional leaders, Pence said his overflight was a type of "freedom of navigation" operation and that it was a message to China that the U.S. "will not be intimidated" by Beijing's warnings against USA operations in areas it claims in the maritime region.