The number of hospitalised COVID-19 patients has risen nearly 50 per cent in the last week and now exceeds 100,000, a Reuters analysis showed, the first time that threshold has been reached since the winter surge a year ago.
Overall, the United States has seen a daily average of 486,000 cases over the last week, a rate that has doubled in seven days and far outstrips that of any other country.
Meanwhile, the Biden administration is finalising contracts for 500 million rapid antigen tests it plans to distribute for free to Americans, the White House said on Tuesday.
The initiative is intended to help alleviate a testing crunch that has led to inadequate supplies and long lines in many places.
"This is about making them free and accessible to the people who want them," White House spokeswoman Jen Psaki said.
The 978,856 new infections on Monday includes some cases from Saturday and Sunday, when many states do not report.
The average number of US COVID-19 deaths per day has remained fairly steady throughout December and into early January at about 1300, though deaths typically lag behind cases and hospitalisations.
Omicron appears to be far more easily transmitted than previous iterations of the virus.
The variant was estimated to account for 95.4 per cent of the coronavirus cases identified in the United States as of January 1, the US Centers for Disease Control and Prevention said on Tuesday.
The World Health Organization said on Tuesday evidence suggests Omicron is causing less severe illness.
Nevertheless, public health officials have warned the sheer volume of Omicron cases threatens to overwhelm hospitals, some of which are already struggling to handle a wave of COVID-19 patients, primarily among the unvaccinated.
Maryland Governor Larry Hogan declared a 30-day state of emergency on Tuesday and mobilised 1000 National Guard members to pandemic response operations as hospitalisations in the state hit a record high of more than 3000.
That is an increase of more than 500 per cent in the last seven weeks, Hogan said.
"The truth is that the next four to six weeks will be the most challenging time of the entire pandemic," Hogan told reporters.
Delaware, Illinois, Ohio and Washington DC, have also reported record numbers of hospitalised COVID patients in recent days.
In Kentucky, where Tuesday's total of 6915 new cases is the highest daily figure since the start of the pandemic, Governor Andy Beshear urged residents to get vaccinated and wear masks.
"Omicron is causing a surge unlike anything we've seen and at this rate our hospitals will fill up," he wrote on Twitter.
More than 325,000 COVID-19 cases among children were reported in the United States for the week ending December 30, according to the American Academy of Pediatrics and the Children's Hospital Association, a new high and almost double the count from the previous two weeks.
