California, the most populous state in the US, is now the epicenter of the COVID-19 pandemic ravaging the country.

Hospitals across the country are reporting shortages of intensive care unit (ICU) beds, and hospitals in California may be in the worst shape.

ICU capacity is at less than 1 percent at hospitals in many California counties, according to state health officials.

In Southern California — which includes Los Angeles County — the availability of ICU beds reached critical mass Thursday, with 0 percent open, health officials said.

When an intensive care unit reaches 0 percent availability, a hospital places patients in beds elsewhere, such as emergency department rooms. But those areas can lack the specialized training of ICU medical professionals. The quality of care can decline, and mortality rates can rise, health officials said.

California reported 52,000 new cases in a single day Thursday — equal to what the entire US was averaging in mid-October — and a one-day record of 379 deaths. More than 16,000 people are in the hospital with COVID-19 symptoms across the state.

Now, there are about 600 new patients with COVID-19 needing hospital admissions daily, and officials said that could rise to anywhere from 750 new COVID-19 patients a day to 1,350 a day by New Year's Eve.

Hospitals are so jammed with COVID-19 patients that they are being cared for at several overflow locations, including temporary field hospitals, a former National Basketball Association arena in Sacramento, a former prison and a college gymnasium. Standby sites include a vacant Sears building in Riverside County.

"I've seen more deaths in the last nine months in my ICU than I have in my entire 20-year career," Amy Arlund, a nurse at Kaiser Permanente Fresno Medical Center, told The Associated Press.

California has brought in more than 500 extra medical staff and deployed them around the state, though most don't have the skills to help in ICUs, officials said. The state said it is seeking a total of 3,000 contracted medical staff members.

Fresno County's hospital system is under so much strain that officials hired an outside team of 31 doctors, nurses and support staff to help treat patients in a makeshift ward.

"There are simply not enough trained staff to care for the volume of patients that are projected to come and need care," Dr Christina Ghaly, Los Angeles County's director of health services, told the Los Angeles Times on Wednesday. "Our hospitals are under siege, and our model shows no end in sight."

Around the country, other hospitals are putting patients in emergency rooms because they have run out of ICU beds. They are moving adults into pediatric hospitals and bringing in staff from out of state to treat the sick in makeshift wards.

In Texas, many intensive care units are either full or approaching capacity. On Wednesday, authorities reported having just over 700 ICU beds open statewide.

In St. Louis, intensive care units are about 90 percent full; hospitals have had to double up patients in ICU rooms and pull nurses out of operating rooms so they could help those who are seriously ill, said Dr Alex Garza, head of the St. Louis Metropolitan Pandemic Task Force.

The pandemic in the US is so widespread that three times as many people are dying each day now than three months ago, and the number of new cases is six times what it was then, according to data from Johns Hopkins University.

On Wednesday, the US logged its latest record-high number of new coronavirus cases in a day — more than 247,000 — and set new daily records for reported deaths and hospitalizations.

New cases on Wednesday were up from 198,357 on Tuesday and surpassed the previous record of 233,133 reported Dec 11, according to Johns Hopkins.

The US also reported 3,656 deaths on Wednesday, according to Johns Hopkins data, surpassing a record 3,306 reported Dec 11. Overall, more than 307,500 people have died of the disease in the US, according to Johns Hopkins data.

Hospitalizations were also at a record high for the 11th day in a row, according to the Covid Tracking Project, which reported 113,090 people in hospitals across the country. That included another record of 21,936 in intensive care.