The U.S. declared a public health emergency in response to the coronavirus that has sickened nearly 10,000 people worldwide.

The U.S. will also temporarily ban foreign nationals from entering the country if they have traveled in China within the preceding 14 days.

"The risk of infection for Americans remains low. With these and previous actions we are working to keep the risk low," said Health and Human Services Secretary Alex Azar.

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American citizens can continue entering the U.S. from Hubei province — the epicenter of the outbreak — but may be quarantined for up to 14 days in a facility.

Other American citizens who have traveled in mainland China but not in Hubei may be self-quarantined in their homes.

These measures will “increase our abilities to detect and contain the coronavirus,” Azar said.

The Centers for Disease Control and Prevention (CDC) has identified six cases of the coronavirus in the U.S. Five of the patients had recently returned to the U.S. after traveling in China. The sixth case, announced Thursday, was the first person-to-person spread of the virus in the U.S.

The patient had contracted the virus from their spouse, who had recently traveled in China.

The declaration came just hours after the CDC announced it would quarantine 195 Americans that were evacuated from China this week.

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The evacuees are being held at an air force base in California for 14 days.

Such precautions are being taken because so little is known about the virus, health officials said.

There currently isn't an accurate test that can determine whether someone has the virus.

Research released this week from Germany indicates someone can spread the virus even if they're not showing symptoms.

"Right now, there's a lot of unknowns. Almost everyday we're learning something we didn't know before," said CDC Director Robert Redfield.

The precautions are intended to prevent the virus from spreading from person to person in the U.S.

Twelve individuals in six countries have contracted the virus but did not travel to China, Redfield said.

Updated at 4:34 pm.