The Centers for Disease Control and Prevention and the U.S. State Department late Monday expanded their travel advisories to cover all of China due to the coronavirus outbreak.

The broader travel alerts come as the U.S. plans to expand screening for the virus to 20 airports from the current five. Details on the additional airports have not been released but Vice President Mike Pence said in a speech Monday that the airports collectively handle 90% of all passengers from China. Houston's George Bush Intercontinental Airport confirmed on Twitter that is is one of the 15 additional airports.

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

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"The outbreak is growing and there is limited access to adequate medical care in affected areas,'' the CDC said in a post on Twitter.

CDC recommends travelers avoid all nonessential travel to #China due to the ongoing #2019nCoV (#coronavirus) outbreak. The outbreak is growing and there is limited access to adequate medical care in affected areas. https://t.co/Km38IKxIAs pic.twitter.com/NHboTImlyr — CDC Travel Health (@CDCtravel) January 27, 2020

The only other country with a CDC Level 3 warning is Venezuela due to shortages of food, water, electricity, medicine and medical supplies.

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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.''

The State Department said anyone who has to visit China should avoid animals (alive or dead) and animal markets, avoid contact with sick people and wash hands frequently with soap and water for 20 seconds.

Private companies are also giving warnings to employees. On Monday, Facebook restricted its employees' travel to China.

What if I have a flight scheduled to China?

On Tuesday, United Airlines became the first U.S. carrier to cancel flights between the U.S. and China, announcing it will suspend 24 flights beginning the first week of February amid growing concern about the spread of the coronavirus that originated in the Asian nation.

"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.

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 Beijing and Shanghai.

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.

It is unclear how the broader government warnings about avoid travel to China will affect their operations, including flights.

CDC officials had strongly suggested in a briefing with reporters on Monday that changes in its travel and screening policies were coming given the rapidly evolving situation.

"I expect that in the coming days our travel recommendations will change,'' said Dr. Nancy Messonnier, director of the agency's National Center for Immunization and Respiratory Diseases.

What happens during those coronavirus airport screenings?

Travelers flying from China to one of the screener airports will be asked to fill out a short questionnaire about their travel, any symptoms, and contact information.

CDC staff will also take travelers' temperatures with a handheld thermometer that doesn't touch the skin and watch for signs of a cough or difficulty breathing. In the case of travelers who appear sick, the CDC will evaluate them further to determine whether the passenger should be taken to a hospital for further care. However, the first two U.S. cases, in Seattle and Chicago, involved travelers who didn't show symptoms at the airport.

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For travelers without symptoms, the CDC is handing out health information cards with details on the symptoms they should look for up to two weeks after leaving China.

China's confirmed cases have ballooned to more than 2,800 since the coronavirus was discovered last month. The epicenter of the outbreak is Wuhan, a city of 11 million people, but more than 40 cases have been confirmed in a dozen other countries, including five in the U.S. According to the CDC, there are 73 more cases under investigation in 26 states.

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Coronavirus quarantines already impacting global tourism industry

In China, the government extended its Lunar New Year holiday period by three days, until Sunday, to ease crowds as tens of millions of Chinese return home from visiting family and tourist sites. At least 17 Chinese cities have imposed lockdowns affecting 50 million people.

There are growing concerns about the travel and tourism impact from the outbreak. In addition to airlines including American, Delta and United, hotels, tourist attractions and other businesses rely on travel between the U.S. and China.

Hotels, airlines, casinos and cruise operators were among the industries suffering the most immediate repercussions, especially with the outbreak occurring during the Lunar New Year, one of the biggest travel seasons in Asia.

What happens in China means a lot more to the world economy than it did when the SARS outbreak struck nearly two decades ago. In 2003, China accounted for 4.3% of world economic output. Last year, it accounted for 16.3%, according to the International Monetary Fund.

About 134 million Chinese traveled abroad in 2019, up 4.5% from a year earlier, according to official figures. Before the outbreak, the China Outbound Tourism Research Institute predicted some 7 million Chinese would travel abroad for the Lunar New Year this year, up from 6.3 million in 2019.

Hong Hong, Thailand, Japan and Vietnam were top destinations, but Chinese tourists are big spenders in cities like London, Milan, Paris and New York.

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Hong Kong stops all rail, ferry service to mainland China

Hong Kong said Tuesday it would cut all links to mainland China as the United States and other governments prepared to evacuate citizens from the Chinese city at the center of a virus outbreak that has now killed more than 100 people.

Carrie Lam, Hong Kong's chief executive, stopped short of a total closing of the border, as North Korea and Mongolia have done, but said that flights from the mainland would be reduced.

The U.S. Consulate in the central Chinese city of Wuhan, where authorities cut off most access Jan. 22 in an effort to contain the disease, was preparing to fly its diplomats and some other Americans out of the city on Wednesday.

Japan and South Korea said they would send planes to Wuhan this week to evacuate their citizens. France, Mongolia and other governments also planned evacuations.

Coronavirus: US says 'do not travel' to Wuhan, China, as airlines issue waivers, add safeguards

Contributing: John Bacon, USA TODAY, Associated Press

This article originally appeared on USA TODAY: Coronavirus screenings to expand to 15 additional US airports