As millions of Americans head to airports for the Juneteenth holiday weekend, many are facing serious travel headaches — including hundreds of flight cancellations and thousands of delays.

The Federal Aviation Administration had imposed a ground delay program at Newark Liberty International Airport — which had a delay of more than two hours, according to FAA's website. An additional ground delay is in place at Philadelphia International Airport, which averaged 45 minutes.

Out west, there's an additional ground delay at Denver International Airport due to thunderstorms, with delays approaching two hours.

As of 6:05 p.m. ET, the tracking site Flight Aware lists more than 6,000 flight delays in the United States and more than 500 cancellations. The site shows the three major New York City airports having the most cancellations.

Transportation Security Administration data show an uptick in passengers being screened at America's airports this week, including more than 2.7 million on Thursday. That number exceeded the passenger volume from 2019 before the pandemic.

TSA officers screened another 2.7 million on Sunday, which was also ahead of 2019 levels.

The Juneteenth holiday combined with Father's Day and pent-up travel demand are likely contributing to the surge.