The White House is expected to advise Americans in coronavirus hotspots to wear cloth masks or scarves in public to help stop the virus spread.
President Donald Trump said such an advisory would not be mandatory.
Residents of New York, the epicentre of the US outbreak, have already been urged to cover their faces in public.
Top health official Dr Anthony Fauci has said he believed all states should issue stay-at-home orders, as the US death toll passed 6,000.
“I don’t understand why that’s not happening,” Dr Fauci told CNN late on Thursday. “If you look at what’s going on in this country, I just don’t understand why we’re not doing that.”
“You’ve got to put your foot on the accelerator to bring that number down,” he added, referring to infection and death rates.
The comments from Dr Fauci, who heads the National Institute of Allergy and Infectious Diseases, appeared to contradict those of Mr Trump, who has consistently dismissed the notion of a nationwide lockdown.
“It’s awfully tough to say, ‘close it down.’ We have to have a little bit of flexibility,” Mr Trump said on Wednesday.
New York City is the worst-hit area, with 1,562 deaths in the pandemic, Johns Hopkins University reports.
Both the US Centers for Disease Control (CDC) and the World Health Organization (WHO) are reassessing their guidance on face masks, as experts race to find ways to fight the highly contagious virus.
Covid-19 is carried in airborne droplets from people coughing or sneezing, but there is some dispute over how far people should distance themselves from each other, and whether masks are useful when used by the public.
The WHO advises that ordinary face masks are only effective if combined with careful hand-washing and social-distancing, and so far it does not recommend them generally for healthy people.
However, more and more health experts now say there are benefits. They argue that the public use of masks can primarily help by preventing asymptomatic patients – people who have been infected with Covid-19 but are not aware, and not displaying any symptoms – from unknowingly spreading the virus to others.
Masks may also help lower the risk of individuals catching the virus through the droplets from another person’s sneeze or a cough – and people can be taught how put masks on and take them off correctly, they argue.
On Thursday New York mayor Bill de Blasio urged all New Yorkers to cover their faces when outside and near others, but not to use surgical masks, which are in short supply.
“It could be a scarf. It could be something you create yourself at home. It could be a bandana,” he said.
“It doesn’t need to be a professional surgical mask. In fact, we don’t want you to use the kind of masks that our first responders need.
Meanwhile, residents in Laredo, Texas will now face a $1,000 (£816) fine if they fail to cover their noses and mouths while outside, after city officials issued an emergency ordinance to its approximately 250,000 residents this week.
Dr Deborah Birx, one of President Trump’s coronavirus advisers, expressed caution about general mask-wearing. “We don’t want people to get an artificial sense of protection,” she said. “They’re an additive.”
There is also disagreement among experts over the benefits of using cloth masks. European advisers say reusable cloth masks are not recommended and may even increase the chance of infection.
Which states are not in lockdown?
At least 297 million Americans in 38 states, the District of Columbia and Puerto Rico have been told to stay home. But the governors of 10 states have so far stopped short of asking all residents to remain indoors.
North Dakota, South Dakota, Arkansas, Iowa and Nebraska so far have no state-wide order urging people inside. “A targeted approach is what is working for us in Arkansas,” said Governor Asa Hutchinson this week. “People are misled by this idea that this stay at home order is magical.”
Iowa Governor Kim Reynolds has argued: “I can’t lock the state down… I can’t lock everybody in their home.”
Other states have left the decision to local officials while still refraining from any state-wide action. Residents in parts of Alabama, Missouri, Oklahoma, South Carolina and Wyoming face some degree of stay home orders, issued by local authorities.
“Our state is so diverse, every segment of the state is different,” said Missouri Governor Mike Parsons this week, defending his reticence to take such action. “It’s very difficult sometimes to just put a blanket order in place.”
“Y’all, we are not California,” said Alabama Governor Kay Ivey to reporters. ” We’re not New York, we aren’t even Louisiana.”
How serious is the pandemic in the US?
In global terms the US has the most Covid-19 cases – more than 245,000. And on Thursday the US authorities said more than 1,000 had died in the past 24 hours – the highest daily toll so far in the world.
Hospitals and morgues in New York are struggling to cope with the pandemic, and New York Governor Andrew Cuomo has warned that New York risks running out of ventilators for patients in six days.
An emergency field hospital now stands in Central Park, and another makeshift hospital is to be set up in the city’s Javits Center, a conference venue.
The White House has ordered car firms to switch rapidly to ventilator production.
More than a million cases of coronavirus have been registered globally, according to Johns Hopkins University.
Nearly 53,000 people have died and more than 210,000 have recovered.
In other developments:
- Spain’s official death toll is 932 for the past 24 hours – just below Thursday’s figure. Spain, with 10,932 deaths so far, is the worst-hit country after Italy for fatalities
- The commander of the USS Theodore Roosevelt was dismissed after saying the US Navy was not doing enough to halt a coronavirus outbreak on board the aircraft carrier
- The Zaandam cruise ship, with dozens of ill passengers on board, docked in Florida after several South American countries refused to accept it
- The World Bank approved a plan to disburse $160bn (£130bn) in emergency aid over 15 months to help countries stricken by the pandemic
- The French authorities have boosted police checks to prevent anyone trying to go on holiday this weekend ahead of Easter
- UK Health Secretary Matt Hancock said the aim was 100,000 tests a day in England by the end of April amid criticism of the government’s plans
- A 4,000-bed emergency field hospital at London’s ExCel centre is due to open later on Friday