The Centers for Disease Control and Prevention on Monday defended what it called "aggressive actions" to control the spread of the new coronavirus in the United States, including stern advisories against traveling to China and mandatory federal quarantines for those arriving from the part of China with the vast majority of cases.

The characterization comes as the agency is working to provide state and local health departments with the tools needed to diagnose the virus themselves.

Currently, the CDC headquarters in Atlanta is the only place in the country with a test for the new coronavirus. That means lab results take at least 24 to 36 hours, including the time it takes to send samples overnight to Atlanta, plus four to six hours to perform the actual test.

On Monday, the CDC said it planned to submit the diagnostics to the Food and Drug Administration for approval of the test under "emergency use authorization." That action hastens the approval process for potentially lifesaving medical or diagnostic products during public health emergencies, the CDC said.

An "explosive" outbreak in China

While cases of the new coronavirus have been diagnosed in at least two dozen countries, including 11 cases in the U.S., by far, China has the greatest number of cases worldwide. As of Tuesday morning local time, Chinese health officials had reported more than 20,000 confirmed cases and 425 deaths.

The CDC called the outbreak in China "explosive" and "unprecedented."

"We are preparing as if this were the next pandemic," Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said during a call with journalists Monday.

She said the Department of State — which last week, issued a "do not travel" advisory for China — is planning to pull out additional U.S. citizens from Hubei province in the coming days. The city of Wuhan, the center of the outbreak, is in Hubei. The first group of evacuees from Wuhan arrived in California last week and remain under federal quarantine.

Full coverage of the coronavirus outbreak

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On Friday, Secretary of Health and Human Services Alex Azar declared the virus a public health emergency in the U.S., and announced that Americans on flights to the U.S. who have been in Hubei province in the last 14 days will be subject to up to 14 days of quarantine.

Those passengers will all be routed through one of 11 airports, including John F. Kennedy International in New York, Chicago's O'Hare, San Francisco International, Seattle-Tacoma International, Daniel K. Inouye International in Honolulu, Los Angeles' LAX, Hartsfield-Jackson in Atlanta, Washington Dulles, Newark Liberty International, Dallas-Fort Worth and Detroit Metropolitan.