Donald Trump's doctor on Monday denied reports that the US president had recently suffered chest pain after he attended an unannounced medical checkup in Washington.

Trump, 73, spent just over an hour on Saturday having "examinations, labs and discussions" at the Walter Reed National Military Medical Center, his physician Sean Conley said in a statement issued by the White House.

"Despite some of the speculation, the President has not had any chest pain, nor was he evaluated or treated for any urgent or acute issues," Conley said.

"Specifically, he did not undergo any specialised cardiac or neurologic evaluations."

Some Washington reports had suggested that the checkup was unscheduled and had been triggered by Trump suffering chest discomfort.

"Due to scheduling uncertainties, the trip was kept off the record," Conley said, describing the checkup as "routine, planned."

The statement included details of the president's cholesterol results and added that after the checkup, Trump had spoken to the family of a soldier undergoing surgery at the hospital as well as to hospital staff.

White House press secretary Stephanie Grisham on Saturday said Trump took advantage of a free weekend to complete part of his annual physical examination before "a very busy 2020" when he faces a tough re-election race.

'Mysterious hospital visit'?

On Monday, the Washington Post ran an editorial casting doubt on the official reason for the medical examination.

Under the headline "Trump's mysterious hospital visit raises many questions", the paper said that US citizens had the right to know about their president's health and if it impacted his work.

"Wasn't his last checkup in February?" the paper asked.

"When did his annual physical become a phased affair? Why was Saturday's visit, unlike previous checkups, not announced or listed on his public schedule?"

On Sunday, the day after the checkup, Trump tweeted that he had started his annual physical examination — reporting "everything very good (great!)"

He added that he would complete the examination next year.

At Trump's last routine examination in February, Conley had declared him to be in "very good health".

Trump, who has confounded health experts with his penchant for junk food and avoidance of strenuous exercise, weighed 110 kg at that time.

In 2018, Trump's then-chief physician, Ronny Jackson, held an unusually detailed press conference in which he declared Trump to have "incredibly good genes".

Soon afterwards, Trump appointed him to lead the Department of Veterans Affairs, before Jackson withdrew his name from consideration.