US President Donald Trump moved to a military hospital for treatment on Friday after being diagnosed with Covid-19 as his administration and re-election campaign scrambled to adjust to an extraordinary twist in his turbulent presidency.

Roughly 17 hours after he announced he had tested positive for the coronavirus, Trump walked slowly from the White House to a waiting helicopter to be taken to Walter Reed National Military Medical Center in Bethesda, Maryland.

He wore a mask and business suit and did not speak to reporters.

"I think I'm doing very well, but...