"I would not be surprised if we go up to 100,000 a day if this does not turn around, and so I am very concerned", Fauci said during his testimony.
Camera IconDirector of the National Institute of Allergy and Infectious Diseases Dr. Anthony FauciÂ wears a face mask as he arrives for a Senate Health, Education, Labor and Pensions Committee hearing on Capitol Hill in Washington, Tuesday, June 30, 2020.
Speaking to the Senate HELP Committee hearing, Fauci said "the Chinese, over the last week or two have identified a virus - in the environment - it has not yet shown to be infecting humans, but it is exhibiting what we call reassortment capability".
"The numbers speak for themselves", Fauci told lawmakers.
Dr Anne Schuchat, principal deputy director of the Centers for Disease Control and Prevention (CDC), warned that the U.S. is not responding like other countries who have shown success in containing the coronavirus, and has allowed the virus to spread much more widely and rapidly.
"There's no doubt that wearing masks protects you", Fauci said.
Committee Chairman Lamar Alexander, R-Tenn., urged people to take CDC guidelines to wear a face covering seriously and lamented the politicization of mask-wearing.
The most prominent individual to refuse to wear a mask, of course, is the president.
"The president has plenty of admirers, they would follow his lead", he added.
Fauci said "there is no guarantee" that ongoing efforts will produce a safe and effective vaccine to prevent infection by the virus, pouring cold water on hopes for a quick fix to the health crisis.
Top health officials also support distributing free masks to Americans.
"But it's something we need to keep our eye out on just the way we did in 2009 with the emergence of the swine flu", he said.
Billions have been poured into Operation Warp Speed, an attempt by the Trump administration to hasten vaccine development and have 300 million doses available by early next year.
FDA Commissioner Stephen Hahn said vaccine makers also must test their shots in diverse populations, including minorities, the elderly, pregnant women and those with chronic health problems. "We have an obligation to use all of our scientific knowledge, regulatory framework to ensure that any vaccine that comes before us, whether for authorization or approval, meets our stringent standards for safety and effectiveness".
In parts of Texas and Arizona, hospital intensive care beds for COVID-19 patients are in short supply.
During the conference, he said about half of all new infections are located in four states. In many states, bar-goers have spread the virus, according to reports.
Asked to forecast the outcome of recent surges in some USA states, Fauci said he can't make an accurate prediction but believes it will be "very disturbing".
Democratic presidential candidate Joe Biden on Tuesday launched a fresh attack on US President Donald Trump's "historic mismanagement" of the pandemic.