The US surgeon general has braced the country for the worsening fallout from coronavirus, warning "this is going to be the hardest and the saddest week of most Americans' lives".
The number of people infected in the US has exceeded 300,000, with the death toll climbing past 8,400.
More than 3,500 of those deaths are in the state of New York.
Much of the country is under orders to stay home, and federal officials said they have seen signs that people are listening to the message about social distancing.
But the Trump administration is also emphasising that the worst is yet to come for many communities.
Surgeon general Jerome Adams told Fox News Sunday: "This is going to be our Pearl Harbour moment, our 9/11 moment, only it's not going to be localised."
He added: "It's going to be happening all over the country. And I want America to understand that."
For most people, the virus causes mild or moderate symptoms, such as a fever and cough that clear up in two to three weeks.
For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.
Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the coming week is "going to be shocking to some".
"But that's what is going to happen before it turns around, so just buckle down," Dr Fauci said on CBS's Face The Nation.
He said the rate of new cases will decide if the United States is putting the worst behind it.
"We've seen that in Italy," Dr Fauci said.
"We're going to hopefully be seeing that in New York very soon and that's the first sign of that plateau and coming down."
Dr Fauci also warned that unless the world gets the virus under control it will "assume a seasonal nature".
"We need to be prepared that, since it unlikely will be completely eradicated from the planet, that as we get into next season, we may see the beginning of a resurgence," Dr Fauci said.
"That's the reason why we're pushing so hard in getting our preparedness much better than it was."
While most states have adopted restrictions on people's movement, a few states have declined to order residents to stay home.
Mr Adams was asked on NBC's Meet The Press if they should join the rest of the country.
"Ninety per cent of Americans are doing their part, even in the states where they haven't had a shelter in place," he said.
"But if you can't give us 30 days, governors, give us a week, give us what you can, so that we don't overwhelm our healthcare systems over this next week."
Meanwhile, President Donald Trump has approved Arizona governor Doug Ducey's request for a major disaster declaration.
Mr Trump's approval opens the door for the state to receive additional federal assistance.
"This continued collaboration will be crucial as we utilise all tools to combat this virus," Mr Ducey said.
A South African leader who inspected IRA arms at a key moment in Northern Ireland's peace process has backed calls for a stimulus package for the continent's nations as their economies struggle during the pandemic.