More than two months after the first peak affected just a handful of states, the virus is cresting again across the South and Southwest.

The US reported Friday at least 51,842 new cases, marking the third day straight with a daily high of more than 50,000 cases, according to data from Johns Hopkins University.

Those who have not given up celebrating America's independence outdoors are finding that beaches in Miami and Los Angeles have been closed, tubing in Texas rivers has been banned and city-sponsored celebrations will be live-streamed.

After crowds were gathering at Myrtle Beach, South Carolina, on Friday, Mayor Brenda Bethune said officials were working to get the message out that masks are needed.

"People spread this virus and we can't stop people from coming here but we all have personal responsibility in helping to prevent the spread of this virus," Bethune told CNN's Jim Acosta.

California, Arizona, Texas and Florida all posted record new cases this week -- Florida reported nearly 9,500 additional coronavirus cases on Friday. Texas had 7,555 new cases after back-to-back days with about 8,000 a piece.

Florida is averaging more new cases per day -- 7,870 -- than any other state, according to a CNN analysis of data from Johns Hopkins University. California and Texas trail close behind.

"There's nothing more American than making a sacrifice by staying home to keep a family member safe, a neighbor safe or a stranger safe," Miami Beach Mayor Dan Gelber told CNN.

Nearly two dozen states have paused their reopenings to combat the spread while others have taken extra measures to keep it out of their borders. New York, New Jersey and Connecticut issued a travel advisory that requires people arriving from eight states with high coronavirus rates to quarantine for two weeks.

Here are other significant developments this week:

Masks alone cannot help combat coronavirus

Some state leaders and experts have blamed the spike in cases on more testing.

"What we're seeing now in the Southwest is a surge in both the number of positive cases and the percentage of people testing who are positive," Dr. Jonathan Reiner, a CNN medical analyst and professor of medicine at George Washington University, said on Friday.

But others experts attributed it to a lack of a comprehensive response.

"If you turn your back on the virus, if you turn your back on science, it's going to bite you," said Dr. Thomas Frieden, the former director for the Centers for Disease Control and Prevention.

The virus, he told CNN, cannot be stopped by a single measure.

"Whether it's restricting travel or staying home or testing a lot of people or wearing a mask. And those are all important, but none of them, in and of themselves are going to control this," he said.

Officials fear July Fourth could bring a surge in cases, and are urging Americans to limit their festivities. The holiday weekend could be the "perfect storm" for new cases, said Dr. Joshua Baroc

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