NEW YORK CITY, New York: U.S. airlines delayed and canceled more than 12,000 flights on April 2 and 3, stranding travelers and causing long waits at airline ticket counters.

The cancellations came amidst the busy spring break travel season and a surge in demand for travel caused by the COVID-19 pandemic.

According to flight tracker FlightAware, more than 3,400 flights were canceled and 8,800 flights were delayed over the weekend.

In terms of the number of flights, the largest U.S. domestic carrier, Southwest, was the hardest hit, canceling 520 flights, or 14 percent of its operation, on April 2, as well as 398 flights on April 3.

In addition to the weather, Southwest, which previously said about 40 to 50 percent of its planes fly through Florida on any given day, admitted it had technology-related issues grounding flights.

According to FlightAware, Fort Lauderdale-based budget airline Spirit had the highest percentage of weekend cancellations, at 27 percent of its April 2 flights, while JetBlue Airways canceled 25 percent of its April 3 flights, after canceling 15 percent of its flights on April 2.

Yamleque Murillo of American Airlines, which canceled 364 April 2 flights and 211 flights on April 3, said the airline was still recovering from the effects of Florida storms.

Texas attorney Erin Chancellor was due to fly from Austin to Greenville, South Carolina early on April 3 for a work conference in Asheville, North Carolina.

However, late on April 2 she received a text alert about a flight change informing her of a 5:15 a.m. departure, an hour earlier than her original departure time and a later arrival, due to a five-hour layover.

In the end, the new flight Southwest Airlines reserved for her was for April 4.

“I was like, oh, this definitely is not going to work. The biggest day at the conference is tomorrow,” she said, as quoted by USA Today.