Three U.S. airlines said Friday they will halt all flights to mainland China.

American Airlines said it will suspend flights beginning Friday. Delta and United said they would end flights in early February.

All 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.

Other international carriers have sharply curtailed or stopped service to China. British Airways, Lufthansa Group, Air France and Lion Air are among the airlines that have suspended service.

In a release announcing the change, Delta said it would operate flights through Wednesday to ensure customers who want to leave China have options to do so. 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.

Until then, the airline will continue to operate select flights to ensure its U.S.-based employees and customers are able to return home. However, the airline will continue operating one daily flight between San Francisco and Hong Kong. American also said it would continue service to Hong Kong.

United will operate its last flight from China to the United States on Wednesday. The last flights from the United States to China will be Tuesday. The airline said it expects to resume service March 28 but will continue to monitor the situation.

More than 200 people — all in China — have died after contracting the virus, and the number of people infected reached 9,720 as of Friday morning, including nine cases in the self-governing island of Taiwan. The State Department has urged Americans not to travel to China.

So far, six people in the United States have been diagnosed with the virus. This week, U.S. health officials expanded the number of airports where travelers will be screened for the virus from five to 20. They say that those most vulnerable are people who have traveled to Wuhan, the epicenter of the outbreak, or who have had close contact with people who have traveled there.

But much is still unknown about the virus and how it might mutate. Health officials believe that precautionary measures, such as the decision to impose a federal quarantine on 195 evacuees who returned to the United States on a flight from Wuhan this week, will help prevent the virus from spreading.

Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention, which is overseeing the U.S. coronavirus response, said officials imposed the quarantine because new cases in China have surged dramatically over the past week. She cited reports that the virus spreads from person to person and sometimes even before the infected person shows symptoms. The virus is spread through respiratory droplets, such as coughing and sneezing.

“If we take strong measures now, we may be able to blunt the impact of the virus on the United States,” she said in a briefing with reporters Friday. “We are facing an unprecedented public health threat.”

On Thursday, the union representing American Airlines pilots filed suit in a Texas court seeking to stop the airline from flying to China, saying the coronavirus posed a threat to crew members and the public.

“Recent events relating to the outbreak of the novel coronavirus in China have created a threat to the safety of passengers and flight crew traveling to and from that country,” said the lawsuit filed on behalf of the Allied Pilots Association, which represents the 15,000 pilots at American.

In a message to pilots, union president Eric Ferguson said pilots should decline any assignment that would take them to China.