Nearly one in four Americans are under orders to close up shop and stay at home, as lawmakers in Washington neared a deal that could pump a record $US1 trillion ($NZ1.76 trillion) into the economy to limit the economic damage from the coronavirus.
New Jersey's governor followed four other states - California, New York, Illinois and Connecticut - that have imposed unprecedented restrictions to slow the spread of infections, which have risen exponentially.
As of midday Saturday (US time), 289 deaths and nearly 23,000 cases had been reported.
Life will not return to normal any time soon, officials warned.
"I don't believe it's going to be a matter of weeks. I believe it is going to be a matter of months," New York Governor Andrew Cuomo said at a news conference.
Federal authorities briefly stopped flights arriving at New York City-area airports after a trainee at an air traffic control centre tested positive.
Meanwhile, the global pandemic closed in on the highest levels of power in the nation's capital.
Two members of the US House of Representatives have tested positive, and US Vice President Mike Pence said he and his wife would be tested after an unidentified aide was diagnosed with the virus. Pence staffers said the aide had mild symptoms and had not had close contact with Pence or President Donald Trump.
Trump tested negative for the virus, his doctor said last week, after dining with a Brazilian delegation that included at least one member who later tested positive.
In Congress, Republican and Democratic leaders said they were closing in on a stimulus bill that would pump $1.4 trillion ($NZ2.46 trillion) into the economy, adding to the hundreds of billions of dollars in fiscal and monetary stimulus that has already been deployed to prop up the world's largest economy.
Senate Republican Leader Mitch McConnell scheduled a vote for Monday.
Hard-hit airlines pressed for $US29 billion ($NZ50.9 billion) in cash, promising in return not to furlough employees before September. But lawmakers said they were inclined to offer loans instead.
"I don't sense support for it here or with the administration," said Senator John Thune, the No. 2 Republican.
State and local officials, meanwhile, said they did not have enough tests to diagnose the disease, protective gear to slow its transmission, and medical equipment to treat those who have contracted it.
"We've gotten no help from the federal government, or limited help," Illinois Governor J.B. Pritzker said at a news briefing.
In New York, Cuomo said the state had identified 6000 ventilators to help sick patients keep breathing, but needed 30,000 more. He said the state is sending one million N95 respirator masks to New York City - short of the three million city officials are seeking.
"We are literally scouring the globe for medical supplies," Cuomo said.
At the White House, officials said they were getting more tests and equipment to where they were needed, but declined to say whether they had delivered 1.4 million tests this week, as promised.
The US Food and Drug Administration approved a test that can deliver a result in 45 minutes, rather than days, according to Cepheid, its maker.
In New York City, where more than 6000 cases have been diagnosed, about a dozen people waited for a test in the parking lot of the Brooklyn Hospital Centre.
"That's insane," city council member Mark Levine said in a phone interview. "If they're well enough to stand in a line, they should be home resting, they don't need a test, and they need to get out of the way."
The number of confirmed cases is expected to skyrocket as testing becomes more widely available, and health officials are scrambling to expand hospital capacity. Dr Anthony Fauci, the US government's top infectious disease expert, urged Americans to postpone non-essential surgeries to keep beds available.
New Jersey became the latest state on Saturday to adopt a statewide directive requiring residents to remain indoors except for trips to grocery stores, pharmacies, gas stations and other "essential businesses".
Stay-at-home orders now apply to 84 million people in states that account for a third of the nation's economy. Other states encouraged residents to reduce activity but did not put restrictions in place. Missouri went in a different direction, allowing child-care providers to take on more children.
The state directives were for the most part issued without strict enforcement mechanisms to back them up.
Cuomo said New York would fine and close businesses that defy the order. Chicago Mayor Lori Lightfoot said police would "admonish" people to go home.
In Ridgefield, Connecticut, where six new cases were reported on Saturday, town official Rudy Marconi said he would dispatch the police to break up a teenagers' basketball game.
"We have no other tools in our toolbox. We have to rely on the social distancing," he said.