People enjoy themselves on the beach on March 4, 2021 in Fort Lauderdale, Florida. College students have begun arriving in the South Florida area for the annual spring break ritual.

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The US could soar again in Covid-19 cases if pandemic safety measures are not followed, the head of the Centers for Disease Control and Prevention warned on Friday.

The nation is seeing a 7-day average of about 57,000 new Covid-19 cases per day, a 7% increase from last week, said CDC Director Dr. Rochelle Walensky during a White House press conference on the pandemic. New hospital stays have increased “slightly” with around 4,700 admissions per day, she said.

“I am still deeply concerned about this development,” said Walensky. “We have seen cases and hospital admissions that have gone from historical declines to stagnations and increases. We know from previous waves that the epidemic curve has real potential to rise again if we don’t control things now.”

The CDC again advised against travel on Monday as business owners in Miami Beach, Florida resented the chaos over the spring break. Miami Beach officials declared a state of emergency and ordered a rare curfew over the weekend to avoid the spread of Covid-19 and stop large crowds and unruly behavior in the popular tourist destination.

US health officials have urged Americans to get vaccinated as soon as possible, especially as highly contagious and potentially more deadly varieties continue to spread. New variants are particularly a problem for public health officials as they could become more resistant to antibody treatments and vaccines.

Last week, White House chief medical officer Dr. Anthony Fauci that B.1.1.7, the highly contagious and possibly more deadly variant first identified in the UK, is likely to account for up to 30% of Covid-19 infections in the US.

As variant cases increase, the pace of vaccination in the United States has increased rapidly, receiving an average of 2.5 million doses per day for the past week, Walensky said. Approximately 87.3 million Americans have received at least one dose of a Covid-19 vaccine, and approximately 47.4 million are fully vaccinated, according to the CDC.

Urging the public to “take this moment very seriously,” Walensky added that people should continue to wear masks, stay 6 feet apart, and avoid crowds or travel. “We can change that, but we all have to work together,” she added.

– CNBC’s Will Feuer contributed to this report.