U.S. President Donald Trump is slamming America's door on most foreign nationals who were recently in Europe — a drastic step in response to an accelerating global pandemic that, should it proceed, could pose a serious threat to commerce and travel between Canada and its largest trading partner.

Trump, in a rare televised Oval Office address, sounded nervous and ill at ease Wednesday as he sought to assure Americans that his White House was taking decisive steps to slow the march of the novel coronavirus.

"To keep new cases from entering our shores, we will be suspending all travel from Europe to the United States for the next 30 days," Trump declared into the camera, his fingers latticed before him on the Resolute Desk.

"There will be exemptions for Americans who have undergone appropriate screenings, and these prohibitions will not only apply to the tremendous amount of trade and cargo, but various other things as we get approval. Anything coming from Europe to the United States is what we are discussing. These restrictions will also not apply to the United Kingdom."

The president later tweeted, "The restriction stops people, not goods."

It wasn't immediately clear how much advance notice the Prime Minister's Office received of the president's plans, or precisely what steps Canada would be taking to deal with the potential fallout.

"We won't comment on other countries' approaches," said PMO spokesman Cameron Ahmad. "We will continue to base our decisions in Canada on science and the best advice from our Public Health Agency."

A news release from the White House clarified the president's proclamation, which was made under the U.S. Immigration and Nationality Act.

It only applies to the movement of human beings, not goods or cargo, and to foreign nationals who in the last two weeks visited one of 26 countries in Europe that allow free and open travel between their borders, a bloc known as the Schengen Area. American citizens and permanent residents are exempt, and will be directed to "a limited number" of airports where they can be screened, the release said.

The ban is scheduled to take effect at midnight Friday night.

Trump, whose efforts to impose travel bans have been met with court challenges in the past, imposed a similar ban in January on recent foreign visitors to China — a restriction he has frequently insisted has helped to keep the outbreak at bay in the United States. A similar ban on foreign nationals who had travelled to Iran came the following month.

The president has been under fire in recent weeks for what critics have called a tepid and disorganized response to the crisis from a White House that didn't appear to be taking the threat seriously.

But with the outbreak escalating, stock markets in freefall and the risk to the U.S. economy growing by the day, Trump — gearing up for a re-election effort later this year — appears to be taking notice.

In addition to the travel ban, he also announced a $50-billion, low-interest plan to improve liquidity in capital markets for small businesses, and to defer tax bills for people and businesses affected by the outbreak. And he's pushing Congress to green-light his proposal to cut payroll taxes to help keep the country's economic gears turning.

After China, South Korea and Iran, Europe is the new source of alarm surrounding what the World Health Organization now considers a pandemic — and Italy, where Prime Minister Giuseppe Conte has effectively locked down his country and shuttered restaurants, retailers, cafes and bars, is the epicentre.

Public gatherings in Italy are currently prohibited and the country's 60 million residents have been asked to limit their travel to work or emergencies to help curb the spread of a virus that has sickened more than 12,000 people and killed 827.

— With files from Mike Blanchfield in Ottawa