US President Donald Trump says he will "most likely" be tested for the novel coronavirus, as questions swirl about why he, his top aides and his family weren't doing more to protect themselves and others after repeated exposure to Covid-19.

President Trump has now had multiple direct and indirect contacts with people who have tested positive for the pandemic virus, which on Friday prompted him to declare a state of emergency as schools and workplaces across the country shuttered, flights were cancelled and Americans braced for war against the threat.

The US leader spent time last weekend at his private club in Florida with a top Brazilian official who later tested positive. And late Friday, news broke that a second person at Mar-a-Lago - who attended a fundraiser with Trump Sunday - tested positive, according to two Republican officials who spoke on condition of anonymity in order to discuss private health matters.

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Several top administration officials, including Attorney General William Barr and Trump's daughter and senior adviser Ivanka Trump, met last week with an Australian Cabinet minister who on Friday was confirmed positive.

Multiple politicians and citizens across the country who have had the same degree of exposure have opted to voluntarily quarantine themselves and get tested out of an abundance of caution.

But Mr Trump, who has long tried to minimise the threat posed by the virus, insisted Friday - contrary to the advice of many medical professionals - that he did not need to isolate himself because he wasn't exhibiting symptoms. He conceded that he would "most likely" submit to testing "fairly soon," but continued to flout public health officials' advice by repeatedly shaking with attendees hands during a Rose Garden press conference on efforts to combat the pandemic.

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Even so, Trump told the nation, "All Americans have a role to play in defeating this virus."

"Anyone can be a carrier for the virus and risk transmission to older Americans and those with underlying health conditions," Trump said, adding, "We must take all precautions and be responsible for the actions that we take and that we see other people take."

The president, according to two people close to the White House, has been reluctant to take the test for fear it would project weakness or worry. Trump has wanted to appear in full control during the crisis, especially as he tries to calm stock markets amid historic drops, and has expressed concerns that taking personal steps could undermine that appearance.

Asked whether he was being selfish by refusing to isolate himself to avoid potentially infecting others and what advice he had for people who may be receiving contradictory messages, Trump said, "I think they have to listen to their doctors."

AFP

Mr Trump spent time last weekend with Brazilian President Jair Bolsonaro's communications director, Fabio Wajngarten, who has tested positive for the virus. Wajngarten posed for a photo with Trump and attended a birthday party held for Kimberly Guilfoyle, who is dating the president's eldest son. Trump and multiple top administration officials were present.

The White House stressed that Mr Trump "had almost no interactions" with Wajngarten while at Mar-a-Lago and therefore did "not require being tested at this time."

Republican officials declined to name the second person who had tested positive at the club and it was unclear how much time Trump had spent with that person.

White House spokesman Judd Deere said Ivanka Trump, who met with Dutton, worked from home Friday "out of an abundance of caution," but said Dutton had been asymptomatic during their interaction, so the White House Medical Unit determined she was "exhibiting no symptoms and does not need to self-quarantine."

Many doctors across the country, however, have been advising those with any exposure to take precautions.

President Trump, who is 73, is considered to be at higher risk of developing serious complications because of his age.