NEW YORK--Delta, American and United said Friday they will suspend all flights between the U.S. and mainland China, following the lead of several major international carriers that have stopped flying to China as the coronavirus outbreak continues to spread.

American and United said they will keep flying to Hong Kong.

American announced that it would stop flying to mainland China starting Friday and running through March 27. Delta and United planned to wait until Feb. 6 to give employees and passengers there more time to leave the country. United's suspension will last until March 28; Delta's until April 30.

All three carriers said they were responding to a sharp drop in demand for the flights and Thursday's U.S. State Department advisory telling Americans not to travel to China because of the outbreak. International experts have labeled the coronavirus a global public-health emergency.

American was under extra pressure after the union representing its pilots sued to halt the flights and told its members not to operate flights to China because of the health risks. The Association of Flight Attendants union asked the federal government to order the airlines to stop China flights.

Several major international airlines, including Air France, British Airways and Scandinavian Airlines, had already suspended service to China. That left U.S. carriers in the awkward position of maintaining China flights while some of their key foreign allies were suspending service. The U.S. airlines gave no explanation for why they waited.

“These are not easy decisions to make,” said Henry Harteveldt, a travel analyst with Atmosphere Research Group in San Francisco. “But if customer demand isn't there, and there is pressure from employees, they didn't have any choice but to suspend their flying.”

As the number of flights in and out of China dwindles, passengers on the planes that are still flying face an eerie scene.

On a flight from Shanghai to New York, nobody spoke for fear of spreading germs, and flight attendants donned masks to serve drinks to passengers, who were also wearing masks. A woman who flew 14 hours from Shanghai to New York said she changed her mask every four hours to make sure it was clean.

Before a flight from Amsterdam to China, frightened passengers protested when they realized that a man from Wuhan, the epicenter of the outbreak, would be on the plane, said Chris Van Heesch, a 50-year old from the Netherlands. In the end, the man was allowed to fly.

At Hazrat Shahjalal International Airport in Bangladesh, passengers arriving from Beijing on Wednesday walked through thermal scanners to check for fevers. As their disembodied faces appeared on a nearby screen, most of their heads looked green, indicating a normal body temperature, but the machine beeped loudly when one man’s forehead appeared red. He was shuttled to the side where a woman took his temperature with a device shaped like a bar code scanner.

“One hundred one degrees,” she called out.

Meanwhile, an airport worker pushed health cards into departing passengers’ hands urging them to contact health authorities if they have a fever within 14 days of arrival.

“The number of infected people in Beijing is relatively low — over 100. But it is much higher in Wuhan," said Mohammed Raihan, a Bangladeshi student who attends Capital Medical University in Beijing. "That's why I've come back. All the schools and universities have been shut down indefinitely.”

A similar scene played out in Kathmandu, Nepal, where masked passengers were greeted with large, illustrated signs imploring them to visit the health desk if they have symptoms including high fever, muscle pain, headaches or hemorrhaging.

Health experts said Thursday there's significant evidence the virus is spreading among people in China and were concerned that in other countries--including the United States, France, Japan, Germany, Canada, South Korea and Vietnam--where there have also been isolated cases of human-to-human transmission. The new virus comes from a large family of coronaviruses, some of which cause nothing worse than a cold.

Airplane cleaners are taking extra precautions. When a plane lands with a passenger showing suspicious symptoms, the cleaning crew will put on face shields, goggles and long-sleeved gowns while they wipe down surfaces with a disinfectant approved by the Centers for Disease Control, said United spokesman Charlie Hobart. If coronavirus is confirmed, the plane will be taken out of service and fumigated, he said.

At New York's John F. Kennedy International Airport, passengers and airport workers wore face masks. Helen Lewis, who helps passengers in wheelchairs, wore gloves and asked coughing passengers to cover their mouths.

“You don’t know who you’re carrying,” said the 62-year-old New Yorker.

Bill Chen, who arrived in San Francisco from Shanghai on Wednesday, said his temperature was screened at the Shanghai airport and he filled out a questionnaire that asked if he had traveled to Wuhan or been in contact with anyone who had.

“I feel a little bit sorry for people traveling on the plane,” Chen said. “People have to be nervous.”

During past outbreaks, including SARS in 2003, U.S. airlines reduced flights to China but did not stop them completely. That outbreak caused Asia-related revenue among U.S. carriers to fall by 20% to 40%, although the business recovered, according to an analysis by J.P. Morgan.

United is widely seen as the most vulnerable to a downturn in China travel because a greater share of its revenue--about 12%, J.P. Morgan estimated--is tied to Asia.

Wolfe Research analyst Hunter Keay estimated that United could lose $629 million in revenue this year if the impact of the outbreak lasts all year. He said United was the most exposed partly because it carries so much corporate travel to China, “which is likely stay on lockdown for some time.” American, Delta and Air Canada would lose between $244 million and $352 million each, he figured.

Shares of United fell 3.8% Friday, while American dropped 3.2% and Delta lost 2.4%.