Donald Trump is in "excellent health," a White House doctor's assessment said on Sunday, after he underwent his first annual medical checkup since returning to the US presidency.

Republican Trump, 78, has repeatedly boasted about his own vigor since starting a second term, while mocking his 82-year-old Democratic predecessor Joe Biden as decrepit and mentally unfit for office.

"President Trump exhibits excellent cognitive and physical health and is fully fit to execute the duties of the Commander-in-Chief and Head of State," read a physician's letter shared by the White House.

It noted only a few abnormalities that included minor sun damage to Trump's skin, as well as scarring on his right ear from a gunshot wound after he was shot at in an assassination attempt last July.

The billionaire told reporters Friday he felt "in very good shape" after his exam earlier that day at the Walter Reed military hospital in the Washington suburbs.

Trump has been accused of a lack of openness about his health despite huge interest in the wellbeing of America's commander-in-chief.

The White House said previously that presidential physician Sean Barbabella would give a readout of the physical and that "of course" it would provide the full report.