ABC News April 3, 2021

Michigan reports highest number of new COVID-19 cases since December

WATCH: Michigan sees alarming rise in COVID-19 cases

Michigan has reported its highest number of new daily COVID-19 cases since early December, as the state is in the midst of a coronavirus surge.

On Saturday, the state health department reported 8,413 new COVID-19 cases. That compares to 1,536 new cases reported one month ago, on March 3.

Cases have been rapidly increasing over the past month, with Michigan now experiencing the "most severe surge of viral spread in the nation," according to the Michigan Health & Hospital Association.

Hospitalizations are also up, particularly among young adults. From March 1 to March 23, hospitalizations increased by 633% for adults ages 30 to 39 and by 800% for adults ages 40 to 49, according to the association.

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A sign requiring face masks and Covid-19 protocols at a restaurant in Plymouth, Mich., March 21, 2021.

"I'm very concerned about what we're seeing in the state of Michigan," Dr. Joneigh S. Khaldun, the state's chief medical executive, told "Good Morning America" this week. "We've seen over the past five to six weeks a significant increase in our cases. Our hospitalizations are going up as well. And we are seeing that younger people, ages 10 all the way up through 60, are getting sick, and many of them are also being hospitalized."

Khaldun pointed to COVID-19 fatigue, including a lack of mask compliance, and gatherings as contributing to the increase.

"I think everyone in Michigan really needs to double down right now," she said.

MORE: COVID-19 is increasing in Michigan. Why it may be a warning.

Gov. Gretchen Whitmer referred to the surge this week as a "compliance, mobility and variant problem."

According to the Centers for Disease Control and Prevention, the state currently ranks second in the nation for the most reported cases of the more transmissible B.1.1.7 variant first discovered in the U.K. As of Wednesday, Michigan has identified 1,468 cases of that variant, according to the state health department.

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UM-Flint nursing student Michaela Dimello gives Burton resident John Ray his first dose of the Moderna COVID-19 vaccine at Bishop Airport in Flint, Mich., March 29, 2021.

Both Whitmer and Khaldun stressed the importance of vaccinations at this time.

"We just have to even more so be laser-focused on our vaccination efforts," Khaldun told "GMA."

Starting Monday, COVID-19 vaccination eligibility in the state expands to all residents ages 16 and older.

MORE: Bidens use Easter message to promote COVID-19 vaccinations

In an interview with Detroit ABC affiliate WXYZ Thursday, Dr. Anthony Fauci, the nation's top infectious disease expert, posited the recent surge "very likely" may be due to Michigan opening up too soon.

"I hesitate to criticize anything the governor did because she's really quite a good governor," Fauci told the station. "I think the idea of pulling back prematurely, under pressure, it's understandable why you might want to do that, but the results, I think, are being manifested in what you're seeing in Michigan."

Among its recently loosened restrictions, the state reopened bars and restaurants for indoor dining on Feb. 1 at 25% indoor capacity, then increased it to 50%, with a maximum of 100 people, on March 5. That day, entertainment venues were also allowed to fill up to 50% capacity.

The state's mask order remains in effect, requiring face coverings in public.