Donald Trump's drive-by stunt has been branded insane "political theatre" by a senior doctor from the same hospital currently treating the US president for a serious coronavirus infection.
Mr Trump left hospital to pay a surprise drive-by visit to the "great patriots" gathering outside the Walter Reed military hospital in Washington.
Seen in a dark face mask while waving to crowds, the president's motorcade rolled past before returning to the hospital.
"We're going to pay a little surprise to some of the great patriots that we have out on the street," Mr Trump said in a video posted to Twitter shortly before his appearance.
"I'm about to make a little surprise visit."
Dr James Phillips, an attending physician at Walter Reed, said the president's actions could only be described as "insanity".
"Every single person in the vehicle during that completely unnecessary presidential 'drive-by' just now has to be quarantined for 14 days. They might get sick. They may die," he wrote on Twitter.
"For political theatre. Commanded by Trump to put their lives at risk for theatre. This is insanity."
Dr Phillips said the risk of transmitting the virus inside the sealed-off presidential car were "as high as it gets".
"That presidential SUV is not only bulletproof, but hermetically sealed against chemical attack," he said.
"The risk of COVID-19 transmission inside is as high as it gets outside of medical procedures. The irresponsibility is astounding.
"My thoughts are with the Secret Service forced to play."
With a tough election campaign against Democratic rival Joe Biden in its final month, Mr Trump and his advisers have done their best to project a sense of continuity.
The president has resumed making calls and tweeting from hospital.
He posted a video Saturday from the business suite in the hospital, saying he was improving and would be "back soon".
In another video he said he "learned a lot about COVID" by "really going to school" as he has battled the virus in hospital.
"This is the real school. This isn't the 'let's read the books school', and I get it, and I understand it, and it's a very interesting thing," he added.
People in Australia must stay at least 1.5 metres away from others. Check your jurisdiction's restrictions on gathering limits.
If you are experiencing cold or flu symptoms, stay home and arrange a test by calling your doctor or contact the Coronavirus Health Information Hotline on 1800 020 080.
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