United Airlines said Tuesday it would suspend 24 flights between the U.S. and China the first week of February amid growing concern about the spread of the coronavirus that originated in the Asian nation.

The airline became the first to make such a move as U.S. officials expanded the number of domestic locations for coronavirus airport screenings from five to 20 and warned Americans to avoid nonessential travel to China.

"Due to a significant decline in demand for travel to China, we are suspending some flights between our hub cities and Beijing, Hong Kong and Shanghai beginning Feb. 1 through Feb. 8," United said in a statement. "We will continue to monitor the situation as it develops and will adjust our schedule as needed."

The affected U.S. hubs include San Francisco International, Newark Liberty International, Chicago O'Hare International and Washington Dulles International.

United said it usually operates 12 flights per day from the U.S. to mainland China and Hong Kong. The planned reduction will mean three or four fewer flights per day.

The Association of Flight Attendants-CWA, representing 50,000 flight attendants at 20 airlines, including United, called the move "a good business decision."

"This is the right proactive approach in times like these," the union's statement said. "We appreciate United’s continued work with our union to mitigate risk during this outbreak."

U.S. officials said Tuesday that five coronavirus cases had been reported in the country, 4,500 cases in China and 60 in other countries. More than 100 deaths have been reported. Still, U.S. officials said that the virus does not pose a significant public health risk to Americans.

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The epicenter of the outbreak is Wuhan, a city of 11 million people.

The CDC issued a level 3 travel warning, its highest level, recommending travelers avoid all nonessential travel to China. Previously only Wuhan was at a Level 3. The rest of China was rated Level 2, which recommends "practice enhanced precautions.''

Separately Monday, the U.S. State Department issued a level 3 alert for China, urging U.S. citizens to "reconsider" travel to China. Last week, it issued a level 4 alert, its highest, for Wuhan. A level 4 means "Do not travel.''

Coronaviruses are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as pneumonia to Middle East respiratory syndrome, known as MERS, and severe acute respiratory syndrome, or SARS.

Common signs of infection include fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause pneumonia, severe acute respiratory syndrome, kidney failure and death.

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What if I have a flight scheduled to China on another airline?

U.S. airlines serving China had already put waivers in place for travelers who don't want to travel to destinations, including Beijing and Shanghai, amid the outbreak, allowing them to postpone or cancel plans without the usual penalty. And they have been expanding the covered dates of travel as the outbreak expands.

Delta, American and United all offer nonstop service between the U.S. and China. American offers five China flights per day in each direction. United operates roughly 12 flights per per day from the U.S. to mainland China and Hong Kong.

The airlines' waivers, terms of which vary by carrier:

Delta: Covers travel to, from or through Beijing and Shanghai through Feb. 29.

American: Covers travel to, from and through Beijing and Shanghai through Feb. 29.

United: Covers travel to, from and through Beijing, Shanghai and Chengdu through Feb. 29.

Contributing: Jayme Deerwester, John Bacon