The coronavirus disease has been reported in all 50 states in the US as at Tuesday evening.
Announcing West Virginia’s first Covid-19 patient, Governor Jim Justice said: “We knew this was coming.” New York City said it was considering a lockdown similar to one in the San Francisco Bay area.
There have so far been 108 deaths in the US from coronavirus and more than 6,300 confirmed cases nationwide.
Globally, there are about 200,000 cases and nearly 8,000 people have died.
“It’s a very, very difficult decision,” Mr de Blasio said. “We’ve never been here before. I have never heard of anything like this in the history of New York City.”
Officials in the San Francisco Bay area have already ordered 6.7 million residents to stay home for all but the most crucial outings until 7 April.
US Vice-President Mike Pence said the White House may call on the US military to establish field hospitals in virus hot spots if requested by state governors.
He told a White House news conference on Tuesday that the Army Corps of Engineers could be asked to set up field hospitals, known as Mash (mobile army surgical hospital) units, or help expand existing hospitals.
Pentagon chief Mark Esper said the US military would make available five million respirator masks and up to 2,000 ventilators to the US health department.
He said the military would also open its 14 certified coronavirus labs to test non-military personnel.
On Tuesday, Florida joined 11 other states in closing bars and restaurants in one of the most subdued St Patrick’s Day celebrations the US has marked in peacetime.
Organisers of the Kentucky Derby – America’s longest continuously held sports event – postponed the horse race until September.It was the latest rite of spring to fall from the calendar because of the coronavirus, along with the Masters golf tournament, the March Madness basketball extravaganza and baseball season.
The country’s largest enclosed shopping centre, the Mall of America in Minnesota, said it would close until the end of the month.