Can Americans in Europe who test positive for coronavirus return to United States soil? It appears the Trump administration was for that before it was suddenly against it.

The president said during his Wednesday night Oval Office address that his 30-day ban on travelers from Europe would include "exemptions for Americans who have undergone appropriate screenings". And guidance the White House released after his primetime address did not mention screening or testing, nor did it describe any quarantine system for Americans to enter into if they test positive.

All it stated was Mr Trump has "determined that it is in the interests of the United States to take action to restrict and suspend the entry into the United States, as immigrants or non-immigrants, of all aliens who were physically present within the Schengen Area during the 14-day period preceding their entry or attempted entry into the United States," a reference to the 26 European countries that have waived all passport and border control measures.

That left questions about just what Americans who are abroad should do if they want to return home.

The vice president, dispatched to clarify and defend Mr Trump's speech and policy ideas on the morning news programs, declared that 'everyone' who is an American citizen or resident would be able to "come home regardless of their symptoms or what their condition is."

Mr Pence, always sounding a more benevolent tone than his brash boss, said any returning American would be asked to enter into "voluntary" quarantine once they land at one of 13 US airports being used in the federal coronavirus response effort.

As frequently happens with even his closest aides, however, Mr Trump soon told reporters the opposite.

"We are not putting them on planes if they test positive," he declared. "It is going to be a pretty strong enforcement of quarantine."

Spokespersons for the president and vice president had not responded to a request for a clarification and an explanation of the actual policy.

Mr Trump and Mr Pence are zeroing in on Europe after the US leader called the continent the "epicenter" of the virus, saying the top breeding ground of COVID-19 had migrated from China and Asia to Europe.

His No. 2 on Thursday told ABC's "Good Morning America" that the administration has concluded "70 per cent of new cases in the world were in Europe.

"And when we looked yesterday at what was then the 35 states where we had cases, about 30 of them could be traced to contacts with Europe," he claimed. "So the president again made another unprecedented decision in suspending all travel from Europe because we essentially want to stop the flow of people bringing the coronavirus here."

A source familiar with the White House's plans essentially repeated the vice president's description then said individuals who test positive or have coronavirus-like symptoms should not fly anyway.

The latest contradictions from inside the West Wing come as the core of the Trump administration's strategy is beginning to come into view. The president and vice president have described a plan to limit the number of individuals entering into the general population who have spent time or hail from countries and areas that have been hit hardest be COVID-19, while also trying to keep people apart to limit the spread at home.

"The key is you have to have separation ... while this thing takes longer to go away," Mr Trump told reporters in the Oval Office during an event with his Irish counterpart.

"I think it is going to work out very well for everybody. But it's a world problem and you do need separation in some cases," Mr Trump added. "You have some areas that are very heavily infected and you have some areas that aren't likely, but we do need separation for a little period of time, in some cases."

The president's tone changed on Monday as he flew back from Florida on Air Force One.

US stock markets were in the midst of their largest one-day drop. That day, he had continued to downplay the risks. But, as aides have acknowledged from the first day of his term, he watches the stock market closely and has sold its record highs as a reason he deserves a second term.

He has repeatedly said the virus is nothing but a flu and likely would "go away" as spring approaches and temperatures warm. But during his Oval Office address and his comments on Thursday, his tone had notably changed.

"So, it's an amazing thing, how fast this one spreads," he said. "This is a very fast spreader."

After cancelling events Thursday and Friday out west, Mr Trump vowed to remain in Washington to oversee the virus response.

"This is the nerve center," he said. "I want to be right here."