Starting Sunday, all flights from China will go through one of these seven airports

Officials also said that Americans who have been in China's Hubei province within 14 days will be subject to a mandatory quarantine period. Americans returning from other parts of China will face enhanced screening and a self-quarantine of up to 14 days.

And starting Sunday, all flights from China will be routed through seven airports, where there will be enhanced health screening.

At a briefing Friday, White House officials said that the risk to Americans of contracting the virus remains low but that they are taking these steps in order to keep it that way. They said the enhanced steps are needed because it has been found that coronavirus can spread by people who show no symptoms, making it much harder to contain.

More than 11,000 people have been diagnosed with the rapidly spreading virus, and more than 210 people, all of them in China, have died. The State Department told Americans not to travel there and advised those already there to consider leaving.

Seven people in the U.S. have been diagnosed with the virus, including a Northern California man who was diagnosed Friday. He had returned to Santa Clara County from Wuhan on Jan. 26. He remains isolated at home. So far, there has only been one case in the U.S. of person-to-person transmission of the virus.

Health officials had recently expanded screening to 20 U.S. airports but now say they will do enhanced screening at seven airports. They are:

Los Angeles International

San Francisco International

John F. Kennedy International

Atlanta's Hartsfield-Jackson International

Honolulu International

Chicago's O'Hare International

Seattle-Takoma International

The new measures comes as air traffic from China has dropped considerably. Officials in China have restricted travel from Wuhan, the city where the virus was first detected at the end of December. On Friday, three U.S. carriers, American, Delta and United, announced they were suspending flights to and from China, though American and United will continue to offer service to Hong Kong.

The temporary lull in air traffic will allow U.S. officials to work out the logistics of how to funnel all incoming flights from China to the seven U.S. airports.

American Airlines began suspending flights on Friday. Delta and United said they will halt service in early February to ensure customers and employees who want to return to the U.S. have that option.

The three carriers had previously announced they would reduce the number of flights but would continue to offer service. On Friday, however, they said the State Department's announcement Thursday evening that it was raising its China travel advisory to Level 4, its highest level of caution, prompted them to reevaluate.

Delta said it will operate flights through Wednesday. The airline's last China-bound flight will leave the United States on Monday. Its last flight from China is set to depart Wednesday. Flights will remain suspended through April 30. American Airlines said that flights would remain grounded through March 28 but that officials would monitor the situation to see whether American would extend the cancellations.

United said it will suspend all operations between its hub cities in Beijing, Chengdu and Shanghai beginning Thursday.