(CNN) Planeloads of Americans fleeing the fast-moving coronavirus outbreak in China are arriving at military bases across the United States this week on what could be the final chartered flights.

The outbreak has infected 28,000 people and killed more than 560 in China , where it started in December in Wuhan city. Outside mainland China, it's raced across continents, infecting more than 250 people in more than 25 countries and territories.

In the US, there are now 12 confirmed cases -- the latest one reported Wednesday in Wisconsin.

350 passengers taken to two bases

Evacuations of Americans from Wuhan started last month as one flight landed at a base in California with nearly 200 Americans aboard.

On Wednesday, two more flights out of Wuhan arrived in California carrying a total of 350 passengers. Both planes landed at Travis Air Force Base -- between San Francisco and Sacramento -- where they were greeted with sack lunches, drinks, fruit and toys for the children on board.

Of those, 178 passengers from one plane stayed at Travis while the other plane refueled before taking the others to Marine Corps Air Station Miramar in San Diego.

Two more evacuation flights are scheduled to arrive from Wuhan later this week -- one headed to Lackland Air Force Base in San Antonio, Texas, and the other to Eppley Airfield in Omaha, Nebraska.

Patients in Texas will be quarantined through February 29 at two hotels on the base, military officials there said. Patients in Nebraska will be quarantined and monitored at Camp Ashland, a National Guard facility about 30 southwest of Omaha, Nebraska Medicine and University of Nebraska Medical Center said in a statement.

A man makes an announcement aboard the evacuation flight that US citizens were on Wednesday.

It's unclear when those flights will arrive in the United States. Both had yet to leave China on Thursday morning, according to public health officials.

The flight bound for Omaha could arrive within the next 24 to 36 hours, officials in Omaha said. The flight headed for San Antonio -- which will transit through Travis Air Force Base -- could arrive on Friday. But officials cautioned that timing was subject to change.

Staff in Omaha are expecting around 70 people while San Antonio is prepared for as many as 250, officials said.

The evacuees were not known to be sick as of Thursday morning, US Centers for Disease Control and Prevention officials said. Their health will be monitored and checked repeatedly during their journeys, and if any show symptoms upon arriving or during the quarantine, they'll be taken to area hospitals for isolation and treatment.

This week's flights will likely be the last ones. The State Department does not anticipate chartering any planes after this week, an official said.

About 1,000 Americans live in Wuhan, and priority on chartered flights was given to US citizens at a higher risk of contracting coronavirus if they stay in the city, the State Department has said.

Four evacuees are being evaluated in San Diego

After landing at Miramar on Wednesday, four evacuees, including a child, were taken to hospitals for evaluation after the CDC said they had a cough or a fever. Officials said they were tested for coronavirus, and the results could be ready as early as Saturday morning.

The evacuees included a 4-year-old girl and her father, who were taken to Rady Children's Hospital, Dr. John Bradley, medical director of the Division of Infectious Diseases at the hospital, said Thursday. The child is asymptomatic while the father has a cough, he added.

"The little girl is so bored," Bradley said, "she's done with one coloring book already and is looking for more."

Two adults were taken to UC San Diego Health, according to Dr. Francesca Torriani, program director of infection prevention. They had mild coughs, Torriani said, and are not related.

If coronavirus is ruled out, the patients will be returned to MCAS Miramar to complete the 14-day quarantine. If tests come back positive, officials will consult with the CDC and local public health officials about next steps.

Passengers placed on quarantine

The CDC is placing passengers arriving from Wuhan under a 14-day quarantine.

Passengers aboard the first chartered flight on January 29 included diplomats and their families. It landed at the March Air Reserve Base in Southern California, and the passengers are under a 14-day quarantine

Before the quarantine, everyone aboard the chartered flights is screened for symptoms before departure and is subjected to additional screenings and monitoring aboard the flight and after landing, the State Department said.

The same applies to Americans arriving on regular passenger flights. US citizens returning from China on commercial flights are being rerouted to one of 11 airports that can handle extra health screenings. Those passengers may be subject to quarantine, according to new federal rules that went into effect Sunday.

The 11 airports -- Honolulu, Los Angeles, San Francisco, Seattle-Tacoma, Chicago O'Hare, Atlanta, Dallas, Detroit, Newark, Washington's Dulles and John F. Kennedy International -- are locations where the Centers for Disease Control and Prevention has the capability to conduct medical screening.