New York and Illinois have followed California in locking down to stem the coronavirus pandemic as US President Donald Trump declared the United States was already "winning" the war despite a rapid rise in confirmed cases and deaths.
The move effectively seals off America's largest cities - New York, Los Angeles and Chicago - with New Jersey also preparing to follow and Connecticut shutting.
However Mr Trump insisted there was no need for a national lockdown, arguing that other parts of the US were not hurting as much as its most populous states.
Governor Andrew Cuomo ordered non-essential businesses to close and banned gatherings in New York state, a day after his counterpart Gavin Newsom told California's 40 million residents to stay home.
"We're all in quarantine now," Mr Cuomo told reporters, warning of civil fines and mandatory closures for anyone violating the order, which takes effect on Sunday evening.
The escalation came as Covid-19-linked deaths in the US rose to 216 - more than doubling in three days - with more than 16,600 confirmed infections, according to a tally by Johns Hopkins University.
Despite the surge, Mr Trump said the world's number one power was "winning" and "going to win this war."
"Those are really two hotbeds. Those are probably the two hottest of them all in terms of hotspots," Mr Trump told the daily White House news conference, adding that states in the American Midwest were not registering as many confirmed cases.
"So no, we're working with the governors and I don't think we'll ever find that necessary," he added.
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However shortly afterwards Illinois Governor JB Pritzker announced an immediate stay-at-home order for the state "to avoid the loss of potentially tens of thousands of lives."
"The only strategy available to us to limit the increase in cases... is to mitigate the spread of coronavirus in the most robust manner possible," he said.
The order is in place from Saturday evening until 7 April, Mr Pritzker added.
The head of the US Army Corps of Engineers, Todd Semonite, said the agency was working on refitting more than 10,000 hotel and dormitory rooms in New York into temporary hospitals to alleviate the burden on health centres.
"We would like to think we can do this in three or four weeks and try to go as fast as we can," he said.
The number of confirmed infections in New York state jumped past 7,000, largely because of an increase in testing, Mr Cuomo said, as he announced he would pass an executive order mandating that only essential businesses can remain open from late Sunday.
He stressed that essential services included grocery stores, pharmacies and food delivery.
Mr Cuomo said that under "Matilda's Law," named after his mother, "non-essential gatherings of individuals of any size" were canceled.
He ordered residents to exercise alone and not hold group activities outside, such as basketball.
He said citizens should avoid public transport "unless urgent and absolutely necessary."
"New York state (is) on pause," he said.
"These actions will cause disruption. They will cause much unhappiness. I understand that," Mr Cuomo added.
He dismissed references to the measures as "shelter-in-place," which they have been called in California, but the rules effectively amount to the same thing.
California's statewide directive, which went into force yesterday evening, also instructs residents to remain at home unless necessary.
It allows petrol stations, pharmacies, banks and laundry services to remain open while restaurants can still provide take-out and delivery.
"They are taking strong steps. I applaud them," Mr Trump said, referring to Mr Cuomo and Californian Governor Gavin Newsom.
Mr Trump also announced that the US and Mexico have agreed to restrict non-essential travel across their border beginning tomorrow.
He said the move, similar to one already announced with northern neighbor Canada, was necessary to prevent the "spread the infection to our border agents, migrants, and to the public at large."
On Capitol Hill, US senators began critical negotiations over a $1 trillion emergency stimulus package to help Americans ravaged by the coronavirus.
Meanwhile a staff member in the office of US Vice President Mike Pence, who is heading the US response to the coronavirus outbreak, has tested positive for the illness, a spokeswoman said.
"Neither President Trump nor Vice President Pence had close contact with the individual. Further contact tracing is being conducted in accordance with CDC guidelines," Mr Pence's press secretary Katie Miller said.