US President Donald Trump has said the nationwide coronavirus emergency could last until the end of the summer or even longer.
He said Americans over the next 15 days should not gather in groups of more than 10 and avoid bars, restaurants, food courts, gyms and crowds.
At the White House, Mr Trump said the country is facing “an invisible enemy” that is “so contagious”.
The US has so far had more than 4,200 cases of the virus and 74 deaths.
There have been more than 174,000 confirmed cases of coronavirus globally and over 6,700 deaths, according to a tally from Johns Hopkins University.
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What are the new US guidelines?
Under the US coronavirus task force’s other new guidelines announced by Mr Trump on Monday:
- All older Americans are urged to stay home, while work and schooling for everyone should be from home
- Discretionary travel, shopping trips and social visits should be avoided and people should stay away from nursing homes or retirement facilities
- Anyone in a household who tests positive for the virus should remain at home along with everyone who lives there
“We’ve made the decision to further toughen the guidelines and blunt the infection now,” Mr Trump told reporters.
“We’d much rather be ahead of the curve than behind it.”
Asked how long the emergency would last, Mr Trump told reporters: “They think August, could be July, could be longer than that.”
White House coronavirus response co-ordinator Dr Deborah Birx, who joined the president, said: “If everybody in America does what we ask for over the next 15 days, we will see a dramatic difference.”
She issued an appeal directly to millennials, asking them to limit social contact even though they are at lower risk of suffering if they contract the virus.
“They are the core people that will stop this virus,” she said. “We really want people to be separated.”
Dr Birx also warned against socialising even if people feel well.
“We know that there is a large group of infected people who are asymptomatic, who continue to spread the virus,” she said.
What else did President Trump say?
The president said he was not considering a national curfew or lockdown, though added: “We may look at certain areas, certain hot spots as they call them.”
Mr Trump told reporters he had not yet decided to close the US-Canada border, but said it was something the administration was considering.
While stocks tumbled, Mr Trump acknowledged there “may be” a recession, but said: “The market will take care of itself.”
As the White House works on a financial assistance package for the beleaguered US airline industry, Mr Trump said it was right to help them.
“It’s not their fault,” he said. A trade group for major airlines said the industry requires more than $50bn (£40bn) in aid to survive.
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The president also addressed issues of testing, as the US has been criticised for lagging far behind smaller countries in getting tests out to the states.
Officials on Monday said a million tests were currently available and more would be coming this week.
“A lot of testing has been going on,” Mr Trump said, though he also noted that those without symptoms should not seek a test.
“Not everybody should run out and get the test, but we’re able to handle tremendous numbers.”
The president, who has been criticised for initially playing down the seriousness of the virus, was asked by a reporter how he would score his administration’s response to the crisis on a scale of one to 10.
“I’d rate it a 10,” he said. “I think we’ve done a great job.”
How are US states responding?
At least 40 US states have declared an emergency over the virus, and 29 states are shutting schools.
Millions of Americans are already working from home and city centres around the country – including Times Square in New York – are drastically less crowded.
On Monday, officials in the San Francisco Bay area issued a sweeping shelter-in-place order affecting nearly seven million people.
San Francisco is placing itself on lockdown for three weeks from midnight on Tuesday. The California city will legally ban residents from venturing out of their homes except to meet basic needs including buying groceries or medicine.
New York, New Jersey and Connecticut announced a tri-state approach to closures, with a shutdown of bars, restaurants, cinemas, casinos and gyms from Monday night for “as long as necessary”.
Pennsylvania, the District of Columbia, Ohio, California, Illinois, Michigan, Massachusetts and Washington state have also advised residents to avoid bars and restaurants.
A Kentucky coronavirus patient has meanwhile been placed under police guard after refusing to quarantine himself.
A local judge declared a state of emergency in order to force a “self-isolation” on the unnamed 53-year-old man.
CNN reports that Mr Trump’s Mar-a-Lago resort in Florida is closed for deep cleaning after several individuals who visited the golf club tested positive for coronavirus.
What about the election?
The outbreak is also disrupting primary season in the US as Democrats hold state-by-state votes to pick a candidate who will challenge Mr Trump in November. It is now a two-man race between Vice-President Joe Biden and Senator Bernie Sanders.
On Tuesday, four states are due to vote: Arizona, Illinois and the key battlegrounds of Florida and Ohio.
But Ohio’s governor has recommended delaying the vote until June, though the other states have said they would continue as scheduled.
Georgia, Louisiana and Kentucky have already postponed their contests due to the virus. Wyoming has suspended its in-person voting.