Nearly a quarter of people in the United States have been ordered to stay at home to slow the spread of the new coronavirus, while regulators approved a diagnostic test that has a detection time of 45 minutes.

As legislators neared a deal that could inject a record sum into the economy to limit the economic damage from the coronavirus, New Jersey followed four other states in imposing unprecedented restrictions amid efforts to curb the transmission of infections, which have risen exponentially.

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New Jersey's directive required residents to remain indoors except for trips to grocery stores, pharmacies, petrol stations and other "essential businesses".

"We can no longer maintain a sense of business as usual during this emergency," said Governor Phil Murphy, adding that "it is no time to panic" but a "time to be smart, proactive, transparent, aggressive".

Stay-at-home orders now apply to 84 million people in five states - California, New York, Illinois, Connecticut and New Jersey - that account for a third of the world's largest economy.

The state directives were for the most part issued without strict enforcement mechanisms to back them up.

Other states encouraged residents to reduce activity but did not put restrictions in place. Missouri went in a different direction, allowing childcare providers to take on more children.

At least 23,941 cases of the novel coronavirus have been reported in the US and 306 people have died from the COVID-19 disease it causes as of Saturday evening, according to a tally of state and local government websites.

Test results in 45 minutes

As hospitals braced for an influx of patients, Anthony Fauci, the US government's top infectious disease expert, urged people to postpone non-essential surgeries to keep beds available.

The Trump administration has struggled to line up tests to diagnose the disease, masks to slow its transmission and medical equipment to treat those who have contracted it.

The US Food and Drug Administration (FDA) approved a test that can deliver a result in 45 minutes, rather than days, Cepheid, its maker, said on Saturday. The California-based company said units would be ready to be shipped next week.

Fast testing is seen as a key part of efforts to limit the spread of the new coronavirus.

The move would be part of a wider effort by federal and state governments and the private sector to rapidly ramp up testing capacities. Other companies say they plan to roll out millions more test units.

The FDA's emergency authorisation for the device came amid a severe shortage of test kits in the US. Governors and health care workers in many states are saying they cannot do enough tests.

"Point-of-care testing means that results are delivered to patients in the patient care settings, like hospitals, urgent care centres and emergency rooms, instead of samples being sent to a laboratory," said FDA Commissioner Stephen Hahn.

'Limited help'

At the White House, officials said they were delivering more tests and equipment where they were needed, but declined to say whether they had met benchmarks they had laid out earlier in the week.

State and local officials say they are scrambling for supplies.

"We've gotten no help from the federal government, or limited help," Illinois Governor Jay Robert Pritzker said at a news briefing.

New York Governor Andrew Cuomo said the state had identified 6,000 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.

In Washington, DC, Republican and Democratic leaders appeared to be approaching a deal to pump more than $1 trillion into the economy, adding to the hundreds of billions of dollars in fiscal and monetary stimulus that have already been deployed to prop up the world's largest economy.

"I think we're clearly going to get there," said Senate Republican Leader Mitch McConnell, who scheduled a vote for Monday.

Hard-hit airlines are pressing for $29bn in cash, promising in return not to furlough employees before September. But legislators said they were inclined to offer loans instead.

Two members of the US House of Representatives have tested positive, and US Vice President Mike Pence and his wife tested negative 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 last week, according to his doctor.