Despite the risk of further spread of the virus, footage shows crowds of people, without masks and not social distancing, chanting, “We love Trump,” outside the Walter Reed Medical Centre where the president is being treated.
Hundreds of people attended the impromptu rally, waving flags and banners supporting Mr Trump’s presidential campaign.
Mr Trump's main doctor, Navy Commander Dr Sean Conley, said in a health update on Saturday night that the medical team treating the president is “cautiously optimistic”, but warned that the president is “not yet out of the woods”.
He said Mr Trump had been up and around at his medical suite during the day and had been conducting business.
Medical experts say the disease can become more dangerous as the body responds to the infection over time.
Mr Trump is expected to remain at Walter Reed National Military Medical Center for several more days.
In a video posted on Saturday from his hospital quarters, Mr Trump said he is feeling better and hopes to “be back soon”.
The president’s diagnosis just a month before the election has thrown his campaign into chaos, with tensions running high across the country.
Rallies in support of Mr Trump have been held around the country, with some of them planned before the president fell ill.
A procession of boats took to the waterways in Fort Lauderdale, in Florida, and in Long Island, California, a pro-Trump caravan of cars covered in slogans and bearing flags drove through the streets.
On Staten Island in New York, hundreds of Trump supporters shouted, “Get well soon,” before launching into a chant of “USA, USA, USA”.
At a rally in Denton, Texas, a pro-Trump supporter was arrested after he was filmed punching a counter-protester in the face after hearing a song with the lyrics “F*** Donald Trump”.
Denton police had asked for the public's help in identifying the man who committed the assault in a Buc-ee's parking lot.
The video, which went viral, shows a man in a hat screaming profanities at the victim and yelling, “Turn it off,” as the anti-Trump rap song by YG appeared to be playing in the background.
The suspect, who was standing with other men who were wearing Trump T-shirts, then punched the victim in the face.
The victim suffered a broken tooth and a wound under his right eyebrow, police said.
The president used his first Sunday morning tweet to say thank you to supporters who rallied outside the Walter Reed military hospital, where he remains.
Additional reporting by agencies
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