“There are a lot of unknowns” compared to influenza viruses, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. “We still have a low risk to the American public but we want to keep it at a low risk.”

The declaration takes effect Sunday and will allow authorities to restrict travel and impose quarantine measures.

American citizens returning from outbreak epicenter of Hubei province in China will be forced into 14 days of mandatory quarantine, officials said at the White House.

Americans returning from the rest of mainland China will undergo additional screening at airports and potential self-administered quarantine.