US President Donald Trump says he is doing well, but that the next few days will be the "real test".
The video, posted on Twitter, comes after mixed messages earlier in the day about his health, after a COVID-19 diagnosis.
The president's physician said that Trump was doing well and had made "substantial progress since diagnosis".
Trump is spending his second night in hospital.
Dr Sean Conley said in a statement that "while not yet out of the woods, the team remains cautiously optimistic" about the president's condition.
A few hours earlier, in the four-minute video message, Trump, dressed in a suit jacket and shirt with no tie, thanked the doctors and nurses at the Walter Reed National Military Medical Centre close to Washington DC, where he is being treated.'
He said he wanted to get back on the campaign trail. Trump faces Joe Biden in the 3 November presidential election.
The president is expected to remain at Walter Reed for a "few days", according to the White House.
However, the White House chief of staff, Mark Meadows, expressed concern about the president's condition, saying he was not yet on a clear path to recovery.
[Source: BBC]
