President Donald Trump issued new guidelines on Monday to help fight the coronavirus, including a recommendation that people avoid social gatherings of more than 10 people, discretionary travel, and going to bars, restaurants and food courts.
Mr Trump said the new guidelines from his coronavirus task force applied for 15 days and were meant to slow the spread of the virus.
"We've made the decision to further toughen the guidelines and blunt the infection now," he told reporters at the White House.
"We'd much rather be ahead of the curve than behind it,"
Mr Trump said the worst of the virus could be over by July, August or later.
"With several weeks of focused action, we can turn the corner and turn it quickly," he said.
Mr Trump said a nationwide curfew was not under consideration at this point.
But he warned the US economy could be heading into a recession.
US stocks fell sharply on Monday as the Federal Reserve's drastic move to cut interest rates to near-zero fueled anxiety over the extent of economic damage from the coronavirus pandemic.
Trading on Wall Street's three main stock indexes was halted for 15 minutes shortly after the open as the S&P 500 index plunged 8 per cent, crossing the 7 per cent threshold that triggers an automatic cutout.
The Dow Jones suffered one of it's worst days, closed down almost 13 per cent, losing almost 3000 points.
Mr Trump has faced criticism for his handling of the pandemic after earlier playing down its seriousness in the early days of the virus' spread.
Canada locks down borders
In Canada, Prime Minister Justin Trudeau announced Monday the country is closing its borders to most foreign travellers, except Americans, in order to slow the spread of the coronavirus pandemic.
"All Canadians, as much as possible, should also stay home," he told a news conference outside his residence where he and his family are self-isolating after his wife Sophie tested positive for the COVID-19 virus.
"We will be denying entry to Canada to people who are not Canadian citizens or permanent residents."
Airlines will be ordered not to allow any passengers with flu-like symptoms to board flights and all inbound international flights will be redirected to four Canadian airports in Montreal, Toronto, Calgary and Vancouver where health screenings will be stepped up.
"As the virus continues its spread, we've decided to take increasingly aggressive steps to keep you and your family safe," Mr Trudeau said, adding that trade would not be affected.
These measures will take effect starting midday on March 18, said Transport Minister Marc Garneau.
US citizens will be exempted from the ban Mr Trudeau said, because of the high "level of integration of our two economies and the coordination that we have."
Canada shares a long unguarded frontier with the United States, which takes 75% of Canadian goods exports.
This "puts the US in a separate category from the rest of the world," he explained.
There will also be exemptions for aircrews, diplomats, and immediate family members of Canadian citizens.
