Minnesota is opening three more free COVID-19 testing centers in response to public concern over the fast-spreading omicron variant and hourlong lines at existing sites.

Gov. Tim Walz said new sites in Anoka, Cottage Grove and North Branch will help increase surveillance of viral spread and alert people to their infection status so they can take steps to protect others.

Even with the expansion, Walz predicted the greatest demand for COVID-19 tests in the entire pandemic in the coming weeks and that some people might struggle to access them.

"I can tell you this from personal experience: What starts out as a sore throat and a little bit of sniffles and a back ache, assume in the environment we are in that that is omicron," said Walz, who was diagnosed with COVID-19 last month despite being fully vaccinated. "Get a test. Find out. ... The sooner you find out, the sooner you are able to isolate and the sooner you are able to break that chain of spread."

Testing slowed over the holidays and that helped to inflate the COVID-19 test positivity rate of 12% in the seven-day period ending Dec. 27. However, Walz and state Health Commissioner Jan Malcolm said Tuesday that a new pandemic wave fueled by omicron could produce unprecedented infection numbers this month.

Hospitalizations might happen in only 2.8% of omicron infections, compared with 3.5% of delta variant infections, based on early federal estimates. But Malcolm said the higher number of total infections could swamp hospitals again anyway.

"We come into the omicron wave ... in a better position than many," Malcolm said of Minnesota and its hospitals, "but even our robust infrastructure is going to be taxed by just the sheer volume of cases we are going to see in the coming weeks."

COVID-19 hospitalizations have declined over the past month in Minnesota, reaching 1,370 on Monday. However, COVID and non-COVID patients have still combined to fill 97% of the state's 1,012 available intensive care beds.

Access to 23 state testing sites recently has been limited. Lines at the Minneapolis Convention Center snaked down the hallway Tuesday afternoon, stretching to a second entrance at the downtown site. Those with appointments were in and out of the testing site within 10 minutes while walk-ins faced long waits. One woman getting her first COVID-19 test complained about waiting for almost an hour, unaware that she could jump to the front of the line because she had an appointment.

Walz on Tuesday said his expansion included another 1.8 million rapid at-home tests to distribute to schools and 150,000 kits to use in communities disproportionately affected by COVID-19. The North Branch site in a former Nike outlet will offer weekday testing starting Monday. Locations and times for the other new sites are pending.

Minnesota has urged broad testing, including for people with no symptoms who have traveled or are visiting people at risk for severe COVID-19. Malcolm said discussions are starting nationally on whether to reserve testing for the neediest people if there is a prolonged shortage.

"The goal will be to continue to make testing widely available to everyone," Malcolm said. "But in terms of making sure that symptomatic folks who are at higher risk categories aren't the ones standing in the long lines? That is something we will continue to work on."

Walz and Malcolm expressed impatience with the Centers for Disease Control and Prevention, which issued a press release last month indicating plans to shorten isolation times from 10 days to five days for people with COVID-19 if they are asymptomatic. Detailed guidance hasn't been released, and Malcolm said it is unclear if people will need negative tests to end their isolation early or whether the lengths will be different for people in different industries.

Michael Osterholm of the University of Minnesota's Center for Infectious Disease Research and Policy said he supported the quicker return-to-work guidance because he expects omicron will infect a lot of health care workers all at once and create workforce shortages.

"Do you want to have somebody there by your bedside in a hospital who is six days post onset of a very mild coldlike illness with an N95 [mask] on taking care of you?" he asked. "Or do you want to lay in your bed for eight hours by yourself? That's the stark choice we have right now."

The 36 COVID-19 deaths reported on Tuesday in Minnesota make December the state's deadliest month of the pandemic in 2021. The 874 deaths reported so far in December exceed the 852 in November and the 775 last January. Minnesota's worst month was December 2020, when vaccine first became available and the state reported 1,800 deaths.

HealthPartners on Tuesday reported that 73% of its 727 COVID-19 hospitalizations in Minnesota and western Wisconsin over the past month involved unvaccinated people. Among the 99 patients placed on ventilators because of severe breathing difficulties, 89% were unvaccinated.

Omicron might produce a lower rate of severe illnesses, but it might end up producing a higher number of severe illnesses because of its broader spread, said Dr. Gregory Poland, head of Mayo Clinic's Vaccine Research Group. He urged people to seek COVID-19 vaccinations and boosters, which reduce the risk of hospitalization by 90%.

"That smaller percentage [of severe illnesses] multiplied against millions means a massive surge in people seeking medical care or having complications from COVID," Poland said. "It's why the hair almost stands up on my neck when I hear people say: 'Oh, omicron is no delta. It's mild.' Well, it is if you've been fully vaccinated and boosted. It might be if you're not, but odds are you're playing Russian roulette and you may not be that lucky."

Staff writers Christopher Snowbeck and Kelly Smith contributed to this report.