Thousands of travelers returning from Europe crowded terminals at several U.S. airports Saturday night in cramped, hours-long lines amid newly implemented heightened coronavirus screening.

The massive lines came hours after the Trump administration's 30-day travel ban on most of Europe took effect. The ban doesn’t apply to American citizens or permanent U.S. residents.

Travelers returning from across the Atlantic were being routed to 13 U.S. airports, including Chicago O’Hare where waits were reportedly as long as eight hours to get through screening for the virus.

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'Safety ... is first & foremost'

Acting Secretary Chad Wolf of the Department of Homeland Security called for patience in a pair of Twitter messages early Sunday.

"DHS is aware of the long lines for passengers who are undergoing increased medical screening requirements. Right now we are working to add additional screening capacity and working with the airlines to expedite the process," he wrote.

He said it takes about one minute for medical professionals to screen each passenger.

"We will be increasing capacity but the health and safety of the American public is first & foremost," he wrote.

Mayor, governor respond

Nevertheless, Chicago's mayor and Illinois' governor, both Democrats, criticized federal agencies' handling of the situation.

Mayor Lori Lightfoot called the O’Hare crowding “unacceptable.”

“The reactionary, poorly planned travel ban has left thousands of travelers at ORD forced into even greater health risk,” she tweeted. @realdonaldtrump and @CBP: no one has time for your incompetence. Fully staff our airport right now, and stop putting Americans in danger.”

Gov. J.B. Pritzker said he had spoken to Lightfoot and the state’s U.S. senators -- Dick Durbin and Tammy Duckworth, both Democrats -- to get the government to resolve the situation.

“The federal government needs to get its s@#t together. NOW,” he pointedly tweeted.

The “enhanced entry screening” includes questions about medical history, current health and contact information for local health officials, according to The Washington Post.

O'Hare's management thanked passengers for their patience. "Customs processing is taking longer than usual inside the Federal Inspection Services (FIS) facility owing to enhanced #COVID19 screening for passengers arriving from Europe," the airport tweeted.

'So close to others'

Meanwhile, similar conditions at the Dallas-Fort Worth airport raised worries about the recommended social distancing measure of at least 6 feet.

“Passengers waited in line for hours at customs at @DFWAirport,” Steven Dial of FOX 4 in Dallas tweeted Saturday night. “Many concerned about being so close to others during the #COVIDー19 outbreak. The airport saying 'CBP officers and the CDC are following federal guidelines to conduct enhanced screening for passengers.'”

Dallas-Fort Worth airport officials also asked for patience.

“Just waiting in a very long line with thousands of people to clear Customs at JFK T4. Not sure who's really taking things seriously,” a passenger arriving in New York City tweeted.

“Friend just returned to Dulles from Amsterdam this evening,” another tweeted. “Crowds were the same! Said if she got the coronavirus it was the 4 hours waiting in that line for just a temp check and told to 'try' and quarantine for 14 days. Outrageous!!!”

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President Trump announced the 30-day European travel ban Wednesday evening during an Oval Office address on coronavirus. The temporary ban on foreign nationals traveling from most European countries went into effect Friday at midnight. On Saturday, the United Kingdom and Ireland were added to the list, effective Monday.