By Madeline Holcombe, CNN

(CNN) -- The number of patients hospitalized across the US with Covid-19 is the highest it's ever been -- and at this rate health experts warn some hospitals may have to ration nurses, respirators and care.

And in Los Angeles County, where a crush of cases have filled hospitals' intensive care units for days, at least five hospitals have already turned patients away because of oxygen supply issues, officials say.

"The surges and the impact on our ICUs across the country is absolutely devastating. ... This is the nightmare scenario we worked so hard to prevent," Dr. Peter Hotez, an infectious disease specialist at the Baylor College of Medicine, told CNN Tuesday about the hospital situation nationwide.

The United States reported 121,235 coronavirus patients in hospitals Monday, the most ever reported on a given day during the pandemic, according to the Covid Tracking Project. The country's proportion of ICU patients who have coronavirus also has shot up, from 16% in September to 40% last week, according to the US Department of Health and Human Services.

"When you run out of capacity, physicians and bioethicists in these hospitals will need to decide which patients are salvageable -- potentially salvageable -- and which patients aren't," CNN medical analyst Dr. Jonathan Reiner said Monday.

December already has been the country's deadliest month of the pandemic. And with travel increasing over the holidays, health experts anticipate the spread of the virus will increase and send hospitalizations surging further.

In Los Angeles County, problems with supplying oxygen to rooms led at least five hospitals to declare an "internal disaster" Sunday, which included turning an unspecified number of patients away, county health services director Dr. Christina Ghaly said.

Though there were multiple issues, the problem generally wasn't an absolute shortage of oxygen, she said. One issue was aging infrastructure pumping the oxygen to patient rooms couldn't keep up with the high number of patients needing it.

She didn't immediately identify the hospitals with those issues. Other capacity issues, meanwhile, are plaguing county medical facilities.

A further spike in cases would put Martin Luther King Jr. Community Hospital in Los Angeles in the position of needing to ration care, CEO Dr. Elaine Batchlor said Monday.

"If we continue to see an increase in the number of Covid patients, we may be forced to do something that, as health professionals, we all really just loathe having to even think about," Batchlor told CNN's Brooke Baldwin.

Battlefield triage techniques

Martin Luther King Jr. Hospital will not turn patients away, Batchlor said, but staff may have to employ techniques that have been used in war.

"We use what in the battlefield is called triage techniques, which is doing an assessment of each person's needs and prognosis and using scarce resources with patients that are most likely to benefit from them," she said.

Already, resources are being used in unconventional ways to accommodate the surge.

"Our staff has been incredibly adept and flexible in accommodating increasing numbers of patients, so as you heard, we have five tents outside of the hospital," Batchlor said. "We have patients in our conference room, in our chapel."

Many gurneys are taken into the gift shop, she said.

While Batchlor didn't specify how many new patients have Covid-19, the increase in their numbers is putting stress on all care.

At Huntington Memorial Hospital in Pasadena, California, nurses that usually care for one or two patients are now caring for three or four, infectious disease specialist Dr. Kimberly Shriner told CNN on Sunday.

"We have a limited number of ventilators, we have a limited number of ICU beds," Shriner said, adding that a team including a bioethicist, a community member, a physician, a nurse and an administrative leader will decide how to divide those resources if it comes down to it.

Ghaly, the county health services director, said some hospitals are attending to patients who are still on ambulances.

"Those patients are being cared for and treated in the ambulance as if it's part of the emergency room bay," Ghaly said.

Fauci: January could be worse than December

January's coronavirus numbers could be worse than in December because travel surged for the holidays, Dr. Anthony Fauci said Tuesday.

He wishes so many hadn't traveled -- but those who did can still decide to limit potential spread, by restricting who they congregate with, he said.

"For those who have already done the travel, the thing to do now is to try to not congregate with large numbers of people in social settings like dinners," Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN's Jim Sciutto on Tuesday.

"Once you get to large numbers of people at a dinner inside, poor air ventilation and circulation, that's when you get in trouble," he said. "That's what we're concerned about -- that in addition to the (the current) surge, we're going to have an increase superimposed upon that surge, which could make January even worse than December."

Air travel has been busy by pandemic standards. Sunday was the busiest day of the pandemic at US airports, when the Transportation Security Administration screened more than 1.28 million people, the TSA said.

And more than 1 million people were screened on seven out of the last 11 days -- the heaviest 11-day stretch since the pandemic started, the TSA said.

Though average numbers of new daily Covid-19 infections and deaths in the US have ticked down in recent days, they are not far removed from all-time highs.

An average of 180,904 daily new infections were reported across the past week as of Monday. The peak average so far -- 219,324 -- was set just 11 days ago.

The US averaged 2,210 new Covid-19 deaths daily across the last week as of Monday, just six days after hitting the peak average of 2,715 a day.

With hospitalizations now at a record, deaths could surge again, as experts say increases in deaths generally follow increases in hospitalizations.

If cases themselves jump with holiday travel, hospitalizations and deaths could soar even further, experts say.

US needs to ramp up vaccines, expert says

As of Monday, about 2.1 million vaccine doses had been administered in the US and more than 11.4 million doses had distributed, according to the US Centers for Disease Control and Prevention.

Another 4.7 million will be distributed by the end of the week, Assistant Secretary for Health at the US Department of Health and Human Services Admiral Brett Giroir said. That would bring the total to more than 15.5 million doses "in the hands of the states."

With doses making their way to state leaders, New Jersey is expecting to vaccinate about 31,000 long term care residents by the end of the week, Gov. Phil Murphy said in a Monday press conference.

"With each passing day, our vaccination program is growing a little larger and a lot stronger," Murphy told reporters. "With the New Year, we are looking forward to the opening of our six vaccination mega sites and the further expansion of our vaccine efforts, and the continued movement through each priority group."

Dr. Ashish Jha, dean of the Brown University School of Public Health, said Monday that the US is falling behind countries like Israel and Canada in the pace of vaccination efforts.

"We really do have to ramp this up," he said. "Things are in a crisis."

Manufacturers like Pfizer have millions of doses that are waiting to be allocated, he said, attributing that problem in part to the federal government not following through with their administration after doses are delivered to states.

"There's a lot of work of getting the vaccine from the state into people's arms, and we needed a clearer set of plans than we've had on that," Jha told CNN's Jim Acosta.