SINGAPORE (REUTERS) - Philippine President Rodrigo Duterte skipped several meetings at the Asean summit in Singapore on Wednesday (Nov 14), prompting the 73-year-old's office to issue a statement scotching speculation that it was due to ill health.

"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," spokesman Salvador Panelo said in a statement.

"The president's constantly punishing work schedule is proof that he is in top physical shape."

Mr Panelo named four scheduled events that Mr Duterte had not attended on Wednesday, during which the President "took power naps" to catch up on sleep, and said he would also skip a gala dinner with the leaders of nine South-east Asian nations, US Vice President Mike Pence and several others.

Mr Duterte's health has been a constant source of speculation since he disappeared from public view for a week last year, and he has said openly that he is tired and would like to step down before the end of his term ends in 2022.

Last month, Mr Duterte's office revealed that he had undergone a colonoscopy and he told reporters that a biopsy had shown he did not have cancer.

The Constitution provides for the public to be told of the state of health of an incumbent president, if serious.

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.

Vice-President Leni Robredo, a leader of the opposition, was elected separately in 2016. Speculation about Mr Duterte's health last month prompted concern that the Philippines could be headed for uncertainty given the highly polarised political climate.

Mr Duterte has cited Ms Robredo's "incompetence" as a reason for his inability to quit as president.

Mr Duterte has a record of skipping summit sessions, though he did not miss any as host when the Philippines held the chair of Asean last year.

Mr Panelo said it was "amusing that some quarters are making a big fuss" of Mr Duterte's absences, noting that he had attended Asean meetings with leaders from China, Japan and Russia.

"Last night, the President worked late and had only less than three hours of sleep," he said. "It is unfortunate that the first event scheduled today was at 8.30am".

Mr Duterte is known for having an unorthodox working schedule that typically starts in mid-afternoon and includes Cabinet meetings that can go on beyond midnight.