The Centers for Disease Control (CDC) issued a Level Three travel health notice on Tuesday, recommending that "travelers avoid all nonessential travel" to China. Level Three is the highest level warning at CDC.

On Monday, the US State Department issued a Level 4 travel advisory for Wuhan, which makes it clear that no American should travel there while the virus continued to have an impact.

Also on Tuesday, the CDC announced that the US will expand screenings for the coronavirus to 15 additional airports, including Houston and Dallas. The implementation of screenings is expected to be set up in the next a few days.

Prior to Tuesday, screening of passengers from China has been conducted at airports in five metropolitan areas — Atlanta, Chicago, New York City, San Francisco and Los Angeles.

In a statement issued Monday, US Vice-President Mike Pence said that the 20 airports "receive 90 percent of all passengers from China. Any passengers who are ill will receive additional screening."

"While it's possible that some person-to-person spread with this virus may be detected in the United States, the goal of the ongoing US public health response is to contain this outbreak and prevent sustained spread in this country," the CDC said in its statement.

The CDC said that so far no person-to-person transmission has been detected in the US.

In addition, it's confirmed that a plane chartered by the US State Department left Wuhan on Wednesday morning local time. It was bound for Ontario, California, a small town 35 miles east of Los Angeles.

The primary mission of the flight was to evacuate roughly three dozen US diplomats and their families in Wuhan. The remaining seats were offered to private American citizens, at a very limited capacity, on a reimbursable basis. The capacity of the plane was estimated to be around 240 passengers.

"All passengers [on the chartered plane] will be subject to CDC screening, health observation, and monitoring requirements," the State Department announced in a statement.

On another front, United Airlines announced on Tuesday that it will suspend flights between China and the US for about a week.

"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.

The affected US 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 US to the Chinese mainland and Hong Kong. According to the reduction, between Feb 1 and Feb 8, three fights to Hong Kong, 10 flights to Beijing, and 11 flights to Shanghai will be canceled.

"We will continue to monitor the situation as it develops and will adjust our schedule as needed," United said in the statement.

In the US, more than 100 people had been screened for the coronavirus. So far, five cases have been confirmed, in Southern California, Arizona, Chicago and Seattle.

Contact the writers at [email protected]. Zong Yi in Washington contributed to this story.