U.S. airports have been beset with long lines of people rushing to return home from Europe.

In Chicago, more than 3,000 people were stuck for hours inside O'Hare airport Saturday.

The delays were due to customs and homeland security screenings for COVID-19 symptoms before passengers were cleared to exit the airport.

Long lines were also reported at some of the 12 other airports allowing flights from Europe.

The crowds also ran counter to U.S. Centers for Disease Control recommendations for people to practice "social distancing" and could have contributed to the spread of the coronavirus, local officials said.

Illinois Governor J.B Pritzker has criticized the administration for not offering more staffing at airports in anticipation of long lines.

Chicago Mayor Lori Lightfoot said Vice President Mike Pence's coronavirus task force did not talk to local officials before starting the screenings.

"Thousands of travelers were forced to wait in exceedingly long lines, congregating in concourses and putting themselves and their loved ones at greater risk of exposure," Lightfoot said.

President Donald Trump asked Americans to pardon the delays.

"We are doing very precise Medical Screenings at our airports. Pardon the interruptions and delays, we are moving as quickly as possible, but it is very important that we be vigilant and careful. We must get it right. Safety first!" he wrote.

Lightfoot said passengers would likely now be kept longer on their planes to manage the flow into the customs area.

Conditions were better Sunday, but lines could again grow as the day progresses and more overseas flights arrive.

With information from the Associated Press.