Sanford, Florida - President Donald Trump returned to the campaign trail on Monday for his first official rally since he contracted the coronavirus, addressing crowds in Florida as he tried to reboot his embattled re-election bid.

"I feel so powerful," Trump (74) told thousands of cheering supporters at the Orlando Sanford International Airport in Florida, joking that he would "kiss the guys and the beautiful women" in the audience.

"It's risky but you gotta get out," the president said, adding he was happy not to be "locked up" anymore.

Trump repeated he was now "immune," despite concerns in the scientific community that immunity in previous Covid-19 patients may be short-lived.

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He praised Florida for being "open for business," again pushed for schools and the economy to reopen and claimed the country was "on track to have 100 million vaccine doses before the end of this year."

Photos showed the president without a face mask as he headed to Florida, a key battleground in the November 3 election.

While Trump has been cleared to hold rallies by his physician, public health guidelines indicate he might still need to remain in isolation to ensure he does not spread the coronavirus.

On Monday, Trump's doctor confirmed for the first time that he had tested negative for the coronavirus, saying it had happened "on consecutive days," but didn't provide further details on the timing.

Data and guidelines by the Centers for Disease Control and Prevention "have informed our medical team's assessment that the President is not infectious to others," Sean Conley said in the statement, released by a spokesperson as Trump was travelling to Florida.

The president is set to hold other major events with supporters this week, including in Pennsylvania, Iowa, and North Carolina.

The US government's top infectious disease expert, Anthony Fauci, told broadcaster CNN on Monday that holding major rallies was "asking for trouble," noting rising caseloads of coronavirus, with a seven-day rolling average of new infections back at around the 50,000 mark.

On Saturday, Trump addressed hundreds of supporters from the White House balcony during his first in-person event since testing positive for the coronavirus. The crowd did not appear to practice social distancing, although many supporters wore masks.

Trump disclosed on October 2 that he had tested positive for the coronavirus and spent three nights in hospital for treatment.

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There was an outbreak at the White House which may have infected dozens, including many of the president's closest aides.

The White House has previously faced criticism for hosting large events where mask-wearing was largely dispensed with, such as a gathering in the Rose Garden in September, after which numerous attendees tested positive.

Trump is trailing Democratic presidential nominee Joe Biden (77) in the polls, and the gap is widening. The Democrat was also on the campaign trail on Monday, and is looking to make inroads into states Trump won handily in 2016, including Ohio.

Biden is out-raising and out-spending Trump on campaign ads, while the president seems to be pinning his hopes on his rallies as he seeks to boost enthusiasm among his base and turn out the vote.

Biden has often criticized Trump's handling of the coronavirus pandemic, which has infected more than 7.7 million people in the United States and led to over 214,900 deaths.

"President Trump comes to Sanford [Florida] today bringing nothing but reckless behavior, divisive rhetoric, and fearmongering," Biden said in a Monday statement.

"But, equally dangerous is what he fails to bring: no plan to get this virus that has taken the lives of over 15,000 Floridians under control."

Trump has tried to shift voters' attention away from the virus, something his own diagnosis made more difficult.

Earlier on Monday, he blasted a group of protestors as "animals,", while urging law enforcement to crack down on demonstrations that included the destruction of property.

"Put these animals in jail, now," Trump said, in one of several early morning tweets.

The president has tried to depict himself as a leader of law and order, following a summer that saw sustained protests against police brutality and racism.

Trump will likely also seek to capitalize on the ongoing nomination hearings of Amy Coney Barrett for the Supreme Court, appealing to conservatives.