The number of COVID-19 patients in care in California has risen 32 per cent in two weeks and intensive-care admissions have spiked 30 per cent, health and human services secretary Dr Mark Ghaly said on Tuesday.

As a result, he said three counties that are home to about 5.5 million people - San Diego, Sacramento and Stanislaus - must reverse re-opening plans and go back to the most restrictive category of regulations.

Under the regime, indoor dining in restaurants is not allowed and gyms and religious institutions are also not permitted to hold indoor activities.

"We anticipate if things stay they way they are ... over half of California counties will have moved into a more restrictive tier" by next week, Ghaly said.

In Minnesota, Governor Tim Walz announced new restrictions amid a fresh record in daily hospitalisations and medical systems in Minnesota expressed concerns about their ability to cope with the surge.

The state reported 1224 hospitalisations on Tuesday, up from 1084 the previous day and a new daily record.

Beginning Friday, restaurants and bars in Minnesota must close dine-in services between 10 pm and 4 am and keep the number of patrons below 50 per cent capacity.

The governor's order also includes private social gatherings, which must be limited to 10 people from three households or less.

"We've turned our dials, we're going to have to turn them back a little bit today," Walz said.

In Illinois, which recorded its highest number of daily cases on Tuesday with 12,626 new infections, Governor J.B. Pritzker said the majority of the state's regions were seeing higher hospitalisation rates than last spring.

Faced with rampant infections and a strained healthcare system, Iowa Governor Kim Reynolds also took steps to curb the disease's spread by limiting the size of social gatherings and imposing mask-wearing.

US Health Secretary Alex Azar expressed concern about strained medical facilities in areas hardest hit by the surge and said officials will set up temporary arrangements where needed.

"As you get more cases, you get more hospitalisations," Azar told MSNBC.

"It's just simple math."

There were just over 59,000 COVID-19 patients in hospitals across the United States on Monday, the country's highest number ever of in-patients being treated for the disease.

Daily new infections exceeded 100,000 for the sixth consecutive day.

Infectious disease expert Anthony Fauci welcomed Monday's news of Pfizer's successful vaccine trials but warned the winter months promise to bring more infections.

Fauci said officials were reporting more infections from small gatherings, an indication the virus is being spread by asymptomatic people.

Australian Associated Press