The U.S. has just 10% of the required respirator masks that would be needed for medical professionals if the COVID-19 outbreak erupts into a "full-blown" pandemic in America.

Health and Human Services official Dr. Robert Kadlec estimates the country would need roughly 3.5 billion of medical-grade N95 masks, which filter out about 95% of all liquid or airborne particles.

"We have about 35 million," Kadlec, assistant secretary for preparedness and response at HHS, said before the Senate Committee on Health, Education, Labor, and Pensions on Tuesday. "Ten percent, and we're actively working on that."

If the U.S. only has 35 million masks and needs 3.5 billion, the math shows the U.S. actually has just 1% of the needed supplies. HHS could not be immediately reached to clarify whether Kadlec misspoke.

(HHS clarified on Wednesday that the United States has about 1%, not 10%, of the required respirator masks that would be needed for medical professionals if the COVID-19 outbreak were to erupt into a pandemic here.)

The comment came minutes after World Health Organization officials called on medical supply manufacturers to "urgently increase production" to meet the global demand that is needed to respond to the COVID-19 outbreak rapidly spreading across the world.

"Supplies are rapidly depleting. WHO estimates that, each month, 89 million medical masks will be required for the COVID-19 response, 76 million examination gloves and 1.6 million goggles," Tedros Adhanom Ghebreyesus, director-general of WHO, said separately at a news conference at the organization's Geneva headquarters. He said manufacturers need to increase personal protective gear supplies by 40%.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, an agency within HHS, told the Senate committee on Tuesday that masks are usually recommended for those who are infected and health-care workers, but not for the general population. The U.S. Centers for Disease Control and Prevention currently does not recommend the use of face masks by the general public to prevent COVID-19.

"The general public who could wear them, that could certainly prevent droplets from someone who is sneezing and coughing on you. The kind of protecting people think it does," he said. "So, therefore, there are some downsides because people keep fussing with the masks."

Health officials have said the respiratory disease is capable of spreading through human-to-human contact, droplets carried through sneezing and coughing, and germs left on inanimate objects.

The Food and Drug Administration and CDC late Monday expanded the types of face masks that can be used by medical professionals during the outbreak.

The FDA said certain masks approved for construction and industrial jobs by the National Institute for Occupational Safety and Health, that haven't been approved by the agency, can be used by the health-care workers in the COVID-19 outbreak.

"Respiratory protective devices are designed to achieve a very close facial fit and very efficient filtration of airborne particles," the FDA said. "When properly fitted, respirators, such as N95s, can filter more airborne particles than face masks, which is important during an outbreak of a respiratory disease like COVID-19."

— CNBC's Noah Higgins-Dunn contributed to this report.

Clarification: This article was updated on Wednesday to clarify Kadlec's comments.