Beijing (CNN) Two flights evacuating US citizens from the epicenter of the coronavirus outbreak in China have departed for the United States, officials from the State Department said.

The travelers were screened for symptoms at the Wuhan airport and will be subject to "Centers for Disease Control (CDC) screening, health observation, and monitoring requirements" when they get to the United States on Wednesday, the State Department said in a statement.

These are the second and third such flights from Wuhan that were arranged by the US government in roughly the past week. The State Department said the three flights had more than 500 passengers.

The latest flights are expected to head to two California military bases: Marine Corps Air Station Miramar in San Diego, and Travis Air Force Base between San Francisco and Sacramento, a US official with knowledge of the matter told CNN.

A spokeswoman for Travis Air Force Base said one of the flights is headed there but didn't have any details on what time it would arrive.

The flights come about a week after the first US government-arranged flight left Wuhan. That first chartered plane, carrying nearly 200 US citizens -- including diplomats and their families -- arrived January 29 at March Air Reserve Base in Southern California.

The Centers for Disease Control and Prevention ordered a federal 14-day quarantine for those evacuees -- the first such order in more than 50 years.

The flights seem to end a few days of uncertainty for the Americans who'd been seeking a way out of Wuhan. A US-arranged flight initially was to depart on Monday, but was delayed , a US official with knowledge of the matter told CNN.

The Chinese government on Monday declined to comment about the delay. But it came as Beijing criticized the United States' response to the coronavirus outbreak, including temporarily denying foreign nationals entry to the US if they had been in China in the previous 14 days.

More than 24,000 cases of Wuhan coronavirus have been confirmed worldwide , including 11 in the United States. At least 490 people have died from the virus.

Even more flights from Wuhan for US citizens could be scheduled. The State Department tweeted it "may be staging flights" on Thursday and interested citizens should contact it by email.

#China: The Dept of State may be staging evacuation flights for US citizens on reimbursable basis leaving #Wuhan Tianhe Airport on 2/6. Interested US citizens with valid passports contact CoronaVirusEmergencyUSC@State.gov. Read this notice before emailing: https://t.co/ivX6xjgLf0 pic.twitter.com/bXn2y0FMtx — Travel - State Dept (@TravelGov) February 4, 2020

Americans who remain in China should take precautionary measures, including "stocking up on food," the State Department said

After the first evacuation flight for US citizens from Wuhan, passengers board buses at March Air Reserve Base in Riverside, California, on January 29.

California father waits to reunite with wife and children

San Diego resident Kenneth Burnett was hoping his wife and two children will be on one of Tuesday's flights, he told CNN on Monday.

His wife, Yanjun Wei, 3-year-old son Rowan, and 1-year-old daughter Mia have been holed up in a high-rise apartment in Wuhan. He was supposed to join them there to celebrate the Chinese New Year, but the outbreak shut the city down, he said.

"It's terrifying. It is very dramatic to shut down (an area) of 50 million people. You think to yourself, if that can happen what else can happen?" Burnett said.

The three were tentatively booked on an evacuation flight out, he said, after he contacted the State Department and the US Embassy in China for help. The children are US citizens; his wife is due to take her citizenship exam this month.

"We think my wife and kids will get seats, but they basically they won't guarantee anything. They'll say maybe the Chinese authorities won't allow it. We know that other countries have not had some of these problems. We feel like other countries haven't felt this problem," he said.

Unions call for feds to engage their groups

Two unions representing flight attendants, teachers and health care professionals called on the federal government Tuesday to provide a more robust and coordinated response to the outbreak.

The White House last week announced the formation of a coronavirus task force.

Sara Nelson, president of the Association of Flight Attendants-CWA, which represents nearly 50,000 flight attendants at 20 airlines, issued a list of demands for the federal government and argued the Trump administration needs to do more to combat the outbreak.

Nelson said she wants the government to engage unions and associations, convene workgroups, issue uniform guidance across industries and distribute materials and supplies to stakeholders.

CNN has reached out to the Department of Health and Human Services and the Department of Transportation for comment on the unions' concerns.