The U.S. government declared the coronavirus outbreak a public health emergency and will ban entry of foreign nationals who recently traveled in China from entering the country starting Sunday at 5 p.m.

Health officials said they made the decision based on all the unknowns about the coronavirus .

"I want to stress the risk of infection for Americans remains low," Alex Azar, the Health and Human Services secretary, said at a press conference Friday. "And with these and our previous actions, we're working to keep the risk low."

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Foreign nationals who have been in China within the past 14 days will be temporarily suspended from entering the U.S., the officials said. Some exceptions will be made for immediate family members of U.S. citizens and permanent residents.

U.S. citizens returning to the U.S. from the Hubei province, which is where the outbreak was first reported, will face up to 14 days of quarantine. Other Americans who visited different parts of China in the past two weeks will undergo health screenings and up to 14 days of self-quarantine at home.

Azar said he hopes the declaration doesn't drastically raise concerns in the U.S.

"I hope that people will see that their government is taking responsible steps to protect them," Azar said. "These are preventive steps. The risk is low in the United States."

The move comes after the World Health Organization declared the outbreak a public health emergency of international concern on Thursday.

China's Foreign Ministry criticized the U.S. response to the virus on Friday after the U.S. government advised against all travel to China.