This is a breaking news update. Below is an earlier version of this story.

U.S. President Donald Trump will extend national physical distancing guidelines to limit the spread of COVID-19 until April 30.

The announcement at the White House on Sunday evening came as many health-care experts worried that Trump would relax restrictions too early after he said he was hoping for an economic resurrection, with the country "raring to go by Easter."

But when asked by reporters about those statements on Sunday evening, Trump said the idea of restoring more normalcy by Easter "was just an aspiration."

This is an earlier version of this story. It has been updated above:

As Americans hunker down for another weekend, President Donald Trump faces a critical choice. The U.S. has topped 120,000 coronavirus cases, the most in the world and by late Monday, the White House campaign of "15 days to stop the spread" will end, leaving an unpredictable president with a critical decision to extend, tighten or loosen the mitigation measures.

"Our country has to go back [to work]," he said Thursday. "Our country is based on that. And I think it's going to happen pretty quickly. A lot of progress has been made, but we've got to go back to work."

His options are complicated. State governments have locked down 169 million Americans in varying stay-at-home orders. Every day, Vice-President Mike Pence, who heads the White House coronavirus task force, has brandished the one-page guidelines for the 15 days, urging compliance with hand washing and physical distancing.

A new mail out to millions of Americans titled "President Trump's Coronavirus Guidelines for America," arrived in mailboxes just before the weekend.

Trump hopes for economic resurrection

Yet Trump has, for a week now, been peddling the idea of allowing more freedoms, hoping for an economic resurrection, with the country "raring to go by Easter."

That statement set off red alarms among health care experts, who strongly urge strict adherence to the restrictions for a longer period.

This weekend the White House's coronavirus task force will present the president with "a range of recommendations and guidance for going forward," said Dr. Deborah Birx, one of the team leaders.

One strategy is to identify if areas in the U.S. that have fewer cases could open up first — the theory being that America could be divided into low-, medium- and high-risk areas.

A woman exits a new coronavirus testing site while others wait in line at Elmhurst Hospital Center in the Queens borough of New York. New York state is the current epicentre of the outbreak in the U.S. (John Mincillo/The Associated Press)

"We may take large sections of our country that aren't so seriously affected, and we may do it that way, but we've got to start the process pretty soon," Trump repeated at a briefing Thursday.

States with fewer confirmed cases, such as North and South Dakota, Nebraska, Wyoming, Montana and New Mexico and pockets in the northeast, could be targeted as lower risk while places such as New York, with nearly half the reported cases, and other hot spots in urban areas would be higher risk.

On Saturday, Trump said he was considering putting sections of New York, New Jersey and Connecticut under quarantine. It was not clear how he would be able to block road, air and sea travel out of a region that serves as the economic engine of the eastern United States, accounting for 12 per cent of GDP.

By Saturday night, he'd retreated from that plan, saying the CDC would instead urge a strong travel advisory to hard-hit areas, and that "a quarantine will not be necessary."

On the recommendation of the White House CoronaVirus Task Force, and upon consultation with the Governor’s of New York, New Jersey and Connecticut, I have asked the <a href="https://twitter.com/CDCgov?ref_src=twsrc%5Etfw">@CDCgov</a> to issue a strong Travel Advisory, to be administered by the Governors, in consultation with the.... —@realDonaldTrump

"I think we can start by opening up certain parts of the country, you know, the farm belt, certain parts of the Midwest, other places," Trump said.

But the job of defending that decision, were it to happen, falls to his coronavirus response team working round the clock to get more data.

"What we're trying to do is to utilize a laser-focused approach rather than a generic horizontal approach. And I think in the 21st century, we should be able to get to that," said Birx, who co-ordinates the White House's coronavirus response team.

"The president's made it clear that, in his words, he wants to open up the country. But we're going to do that responsibly."

Muddling the public health message

After declaring himself a "wartime president," the president appeared impatient this week with the economic casualties, including 3.2 million unemployed, cratering growth and a kick to a stock market that was soaring just a month ago.

Friday, he seemed to lean toward public health advice, telling a briefing, "life and safety and then the economy."

But health professionals and state officials are deeply worried he will muddle the public health messaging.

"I am quite concerned that we're considering these measures, especially when the science doesn't support it," says Nadia Abuelezam, an infectious disease epidemiologist and assistant professor at Boston College's Connell School of Nursing.

"Even if we do see a reduction in the number of cases, that doesn't mean that it can't re-surge there or it can't be reintroduced to that particular area."

A sign at the international border crossing that connects Windsor, Ont., and Detroit warning of the ban on non-essential travel between Canada and U.S. that is currently in place because of the coronavirus pandemic. Travel restrictions between states would be harder to enforce, say some experts. (Rebecca Cook/Reuters)

It's not at all clear how some states with fewer cases could open up while neighbouring states with a higher incidence remain locked down. Confusion over what's allowed where could prompt people to pay less heed to the restrictions, health experts fear.

"Viruses do not respect borders. Viruses do not discriminate. Viruses just want to find another body where they can replicate. And I think that's something to really keep in mind," said Abuelezam.

More data needed

Infectious disease experts want more time to measure if the mitigation efforts across the country are working. They also want to better understand how many Americans have or had the virus, with few or no symptoms.

That data would help more accurately define how much coronavirus is circulating in the community, but capturing that picture is still extremely complicated and will take time.

"I understand the concept — we're hearing of 'pockets' [of no coronavirus]. But the problem with those pockets is we don't know if those are places where the disease just hasn't spread or testing hasn't started," said William Jaquis, president of the American College of Emergency Physicians, in an interview with CBC News.

"Look, we all had low cases at one time, right? And then Seattle started, then New York started, New Orleans, now Detroit, and California is ramping up."

The USNS Mercy docks in San Diego on March 18. The 1,000-bed naval hospital ship will be used to help combat an expected shortage of hospital beds in Los Angeles as the virus spreads. A second ship was sent to New York. (Gregory Bull/The Associated Press)

Modelling the new virus and predicting its effect on large populations is challenging, and changing, but data from more tests will ultimately produce a clearer picture.

"It's really important to remember that … the mathematical modelling results that are coming out about the United States, are all indicating that if we let up on the [physical] distancing now, we will see a large spike in the number of new cases," said Abuelezam.

40% of U.S. has low number of cases: Birx

The coronavirus team at the White House is collecting as much data as fast as it can to provide concrete evidence to persuade an unpredictable president, who has a habit of freestyling from the podium.

Birx's role at the daily briefings is to balance the bad news piling up as the cases mount and the slope of the virus goes straight up, with no levelling off.

You know, it's one thing to have it. It's another thing to die - U.S. President Donald Trump

"Nineteen out of 50 states that had early cases have persistently low level of cases, at this point less than 200 cases [on Thursday]," she said. "So, that's almost 40 per cent of the country with extraordinarily low numbers, and they are testing.

"Models are models. We are adapting. There is enough data now of the real experience with the coronavirus on the ground to really make these predictions much more sound."

Trump has seemed persuaded that the number of deaths does not justify shutting down the whole of the country for longer than a few weeks.

Nearly empty on- and off-ramps viewed from the roof of the Space Needle in downtown Seattle, a city that, like several others across the U.S., is under a stay-at-home order because of the coronavirus pandemic. (Ted S. Warren/The Associated Press)

"In my opinion, the mortality rate, it's way, way down, and that takes a lot of fear out. You know, it's one thing to have it. It's another thing to die," he said.

"When I first got involved, I was being told numbers that were much, much higher than the number seems to be. That's one of the reasons I say, look, we're going to beat this, and we're going to get back to work."

States enforcing federal guidelines differently

Practically, Trump does not have the powers to regulate whether businesses open or close. The U.S. states can independently decide which restrictions will apply under broader federal guidelines.

On Friday, one of those lower-risk states, Wyoming, extended its closures of schools and some businesses to April 17.

"It's clear how important it is for us to take sustained action," said Governor Mark Gordon.

With the U.S. now eclipsing cases in all other countries, the experience on the ground changes by the hour and the health-care response in some hard-hit areas is severely strained.

Elena Likaj, prevention department manager at Odyssey House Louisiana , which runs a drive-through COVID-19 testing site in New Orleans, takes the temperature of cyclist Peyton Gill. Louisiana has the third-highest number of virus-related deaths in the U.S. after New York and Washington. (Kathleen Flynn/Reuters)

Nurses and doctors say they can't get enough personal protective equipment. Ventilators now being raced into production might not come soon enough. States are competing with each other to procure supplies.

The number of cases is one marker, but the rate of growth is even more telling, said Jaquis. In New York, cases doubled in three days.

Doctors say they need more time to allow them to respond to what's about to hit, without worrying about the second wave of spread.

Improvised hospital rooms at the Jacob K. Javits Convention Center in Manhattan , which will be partially converted into a hospital for patients affected by COVID-19. New York is preparing for an anticipated increase in COVID-19 cases needing hospitalization in the coming weeks. (Jeenah Moon/Reuters)

"We're not quite ready to take care of what's coming," Jaquis said. "And we need to make sure that all of our patients and our communities and our health-care workers are protected. So right now, we need people to continue to stay home and we need to flatten that curve. They just need to continue with this for longer."

Trump, calling himself a "wartime president," travelled Saturday to Norfolk, Va., to offer a "kiss goodbye" to the USNS Comfort, a naval hospital ship headed for New York harbour to help the city's health care workers deal with the pandemic.

"It sends a great signal," Trump said, "when the president is able to go there and say thank you."

Perhaps a confusing signal for the millions of Americans under orders to stay at home.