Americans should get ready for a 9/11 and Pearl Harbor-type death toll in the coming week as coronavirus kills a "shocking" number of people, United States officials have warned.

The nation's top doctor, Surgeon General Jerome Adams, said Americans should brace for levels of tragedy reminiscent of the September 11, 2001 attacks and the bombing of Pearl Harbor in 1941.

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"This is going to be the hardest and the saddest week of most Americans' lives, quite frankly," Adams said on Sunday.

"This is going to be our Pearl Harbor moment, our 9/11 moment, only it's not going to be localised. It's going to be happening all over the country. And I want America to understand that."

Nearly 3,000 people were killed in the US in the September 11 attacks carried out by al-Qaeda. More than 2,400 Americans died after Japan hit the Pearl Harbor naval base.

'Buckle down'

Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the death toll in 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".

Fauci said the virus probably will not be wiped out entirely this year, and unless the world gets it under control, it will "assume a seasonal nature".

"We need to be prepared that, since it is unlikely will be completely eradicated from the planet, that as we get into next season, we may see the beginning of a resurgence," Fauci said.

"That's the reason why we're pushing so hard in getting our preparedness much better than it was."

For most people, the virus causes mild or moderate symptoms, such as 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 severe pneumonia and death.

Stay at home

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. A few states, however, have declined to issue such orders.

Adams pleaded with those states to join the rest of the country.

"Ninety percent of Americans are doing their part, even in the states where they haven't had a shelter in place," Adams said. "But if you can't give us 30 days, governors, give us, give us a week, give us what you can, so that we don't overwhelm our health care systems over this next week."

Arkansas Governor Asa Hutchinson, who has not issued a stay-at-home order, said federal officials who have urged them are "just looking at the nation as a whole".

"But whenever you look at our state, I think Dr Fauci would be very pleased with the fact that we are beating some of our other states in reducing the spread and the commitment that we have to working every day to accomplish that," Hutchison said.

Illinois Governor JB Pritzker, who was among the first in the nation to issue orders that his state's residents stay at home, suggested the federal government should step in and make the remaining states follow suit.

"This virus knows no borders. And so it was up to the federal government, to begin with, to advise and to ask all the governors to put in stay-at-home orders," Pritzker said.

"Those governors, Republican governors, would have done it much earlier if the president had suggested it much earlier."

US President Donald Trump suggested the hard weeks ahead could foretell the turning of a corner. "We're starting to see light at the end of the tunnel," he said at an evening White House briefing.