Nearly one in four Americans are under instructions to stay home, as a fifth US state imposes restrictions on residents.
The curbs are aimed at reducing the spread of COVID-19, the illness caused by the coronaviruswhich is sweeping the world.
A major disaster has also been declared in New York, freeing up access to billions of dollars in relief funding.
Already more than 300,000 people globally have been infected and almost 13,000 have died. In the US the number of confirmed cases is more than 25,000, with more than 300 people dead.
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New Jersey has joined California, New York, Illinois and Connecticut in telling residents to stay home, while many other states have urged people to avoid large gatherings.
West Virginia Governor Jim Justice warned residents to take the threat seriously, adding: “It’s like we are all lost in a movie that we can’t relate to in any way.”
Some 84 million people in the US can now leave their homes only to visit grocery stores, pharmacies, petrol stations and other “essential businesses”.
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But the consequences of breaching the rules appear minimal in many cases.
In New York, governor Andrew Cuomo said businesses could be fined and forced to close, while Chicago mayor Lori Lightfoot said police would “admonish” people.
The Trump administration is still struggling to get enough tests for the disease, masks to protect those trying to treat it, and medical equipment to help those suffering as a result of it.
Illinois Governor JB Pritzker said: “We’ve gotten no help from the federal government, or limited help.”
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Mr Cuomo said New York needs 30,000 more ventilators, adding: “We’re literally scouring the globe for medical supplies”.
Some 6,000 cases have been diagnosed in New York City alone, including at least 38 in the city’s jails. At least another 58 people in the prison system are being monitored.
Two members of the US House of Representatives have tested positive for the disease but Vice President Mike Pence and his wife have tested negative after one of his aides was diagnosed as having the illness.
Meanwhile, US politicians are edging closer to approving $1trn (£860bn) economic stimulus aimed at supporting the world’s largest economy through the crisis.
Despite the pleas of airlines, however, they are likely to have to make do with loans, rather than grants.