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WASHINGTON — The director of the Centers for Disease Control and Prevention said Friday that as parts of the U.S. seek to reopen amid the coronavirus outbreak, people should still be vigilant by practicing social distancing, wearing face coverings and washing their hands.

“It’s important not to let up at all,” CDC Director Robert Redfield said in an interview on NBC’s “Today” show.

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Those in areas where there are still significant ongoing transmissions, such as New York, Boston, Baltimore and Washington, should continue following the mitigation strategies recommended by the federal government, Redfield said.

“We need to be very vigilant in that this new opening up — which has that requirement of early case diagnosis and isolation, contact tracing — is really embedded, as you'll see in the phases, with still maintaining that personal vigilance, that personal mitigation, so that we can continue to limit and protect the vulnerable in this nation,” he said.

Redfield was referring to a plan unveiled by President Donald Trump and the White House coronavirus task force on Thursday that outlined recommendations for how governors can reopen their state economies. The plan lays out three phases by which states could direct the reopening of businesses, restaurants and other places based on evidence that the number of positive COVID-19 cases and hospital capacity have decreased.

The reopening of the country should be a “step-by-step, prudent process,” Redfield said Friday.

Trump said Thursday that governors could decide to reopen their states on May 1 or even earlier. On Friday, Redfield suggested there are a number of regions that are already prepared to makes those moves.

The U.S. has “very good surveillance systems” that look at flu-like and respiratory illnesses, he said, adding, “We’re seeing all of those drop substantially, so there are a number of jurisdictions that have limited activity.”