US President Donald Trump has said the nationwide coronavirus emergency could last until the end of the summer or even longer.
He said Americans over the next 15 days should not gather in groups of more than 10 and avoid bars, restaurants, food courts, gyms and crowds.
At the White House, Mr Trump said the country is facing "an invisible enemy" that is "so contagious".
The US has so far had nearly 4,500 cases of the virus and 78 deaths.
There have been more than 180,000 confirmed cases of coronavirus globally and over 7,100 deaths, according to a tally from Johns Hopkins University.
