The US has recorded more than one million new Covid-19 cases, as officials warn the peak of a fast-spreading Omicron surge is still to come.
A record 1,080,211 cases were reported on Monday - the highest one-day tally of new cases anywhere in the world, according to Johns Hopkins University.
The Omicron variant accounts for the majority of cases in the US.
The top US pandemic adviser Anthony Fauci has said the country is facing "almost a vertical increase" in cases.
He said the peak may be weeks away.
While rates of death and hospital admissions in the US have been far lower in recent weeks than in previous infection spikes, the number of hospital admissions has been steadily rising.
But Dr Fauci said the example of South Africa - where Omicron first spread rapidly before subsiding - offered some hope.
Omicron has also led to school districts across the country postponing the return of students to classrooms following the winter break due to the rapid spread of the variant and subsequent staffing shortages. There are also concerns over challenges in securing rapid tests for students and teachers.
In Detroit, Michigan, for example - which is experiencing an all-time high infection rate of 36 percent - city school officials announced that schools will remain closed through Wednesday.
A number of other major school systems, including Atlanta, Milwaukee, Cleveland, and Newark, have announced postponements or a return to virtual classes.
In New York City, the largest school district in the US, schools remained open. On Monday, Mayor Eric Adams said that school is "the safest place or our children".
The New York Times reported, however, that approximately one third of parents kept their children at home over Covid-19 fears.
In terms of hospital admissions, data from the US Department of Health and Human Services shows that more than 103,000 people are currently in hospital with Covid-19 - the first time the tally has crossed the six-figure mark since September.
State health officials have reported that the vast majority of Covid-19 hospital admissions are among the unvaccinated. In Illinois, for example, officials over the weekend said that nearly 85 percent of patients with Covid-19 or related diseases are unvaccinated.
"I'm still very concerned about the tens of millions of people who are not vaccinated at all because even though many of them are going to get asymptomatic and mildly symptomatic, a fair number of them are going to get severe disease," Dr Fauci told the ABC on Monday.
Officials have also said that the number of children in hospital is rising.
Some 8652 people are reported to have died from the disease in the past week, according to Johns Hopkins.
The previous US record of cases was 590,000, reported four days ago.
The highest number outside the US came during India's Delta surge, when more than 414,188 people were confirmed as having the disease in May 2021.
Studies suggest that Omicron is milder than the previously dominant Delta variant, but fears remain that the sheer number of cases stemming from the highly infectious Omicron could overwhelm hospitals.