(CNN) The Transportation Security Administration (TSA) issued a new directive effective Sunday requiring airlines to ask passengers on flights from outside the United States if they've been to mainland China in the past 14 days.

The directive comes as the Wuhan coronavirus, which was first detected in China in December, continues to spread around the world. The virus has killed 304 people in mainland China , one man in the Philippines and infected more than 14,000 in over 20 countries and territories.

In the United States, an eighth case of coronavirus has been confirmed -- a Boston college student in his 20s, health officials said Saturday.

Chinese nationals coming from China and connecting through another foreign airport will be denied travel, according to a person briefed on the new restrictions. Those with pre-clearance are exempted.

The TSA notified airlines about the restrictions Saturday, a day after the White House announced plans to set up new travel rules . The directive to both US and foreign airlines goes into effect at 5 p.m. ET Sunday.

"Under these directives, non-US citizens who have been in China within 14 days of their planned travel will not be permitted to fly to the United States," TSA administrator David Pekoske said in an email directive sent to employees Saturday.

"US citizens who have been in China within 14 days of their planned travel will be permitted to enter the country through one of seven airports -- Honolulu, Los Angeles, San Francisco, Seattle-Tacoma, Chicago O'Hare, Atlanta, and John F. Kennedy International airports -- where the Centers for Disease Control and Prevention has the capability to conduct medical screening. This applies to travel from any airport with direct flights to the US, not just airports in China."

In addition to the directive, Pekoske said, all frontline employees will be permitted to wear surgical masks if they choose to do so.

The US declared coronavirus a public health emergency on Friday.

Once the declaration goes into effect at 5 pm ET Sunday, US citizens returning to the United States who've been in China's Hubei province in the two weeks before their return will be subject to up to 14 days of mandatory quarantine.

US citizens returning from the rest of mainland China in the two weeks prior will face a health screening. They will also get up to two weeks of monitored self-quarantine to ensure they pose no health risk.

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