United Airlines airplanes sit parked in Newark, New Jersey, on June 1. United Airlines halted its mainline flights out of departure airports on August 6 due to a “technology issue.” (Photo credit: Gary Hershorn/Corbis News/Getty Images via CNN Newsource)

(CNN) — A “technology issue” that prompted United Airlines to ground flights across the US on Wednesday, triggering more than 1,000 delays and dozens of cancellations, has been resolved, the airline told CNN.

The outage, which began at 6:12 p.m. ET and was resolved within a few hours, stemmed from an issue with the airline’s weight and balance computer system, known as Unimatic, and was unrelated to recent cybersecurity concerns in the industry, the company said. It’s not clear what caused the problem.

“The underlying technology issue has been resolved and while we expect residual delays, our team is working to restore our normal operations,” a United Airlines spokesperson told CNN on Wednesday night.

According to flight data tracker FlightAware, more than 1,000 flights had been delayed and hundreds canceled from Wednesday evening into Thursday morning.

The Federal Aviation Administration acknowledged the disruption, saying, “We’re aware United experienced a technology issue disrupting their operations. Some delays may continue as they work through the recovery process.” The FAA is helping address United’s “flight backlog and remain in close contact with United.”

Airports in Chicago, Denver, Newark, Houston and San Francisco were impacted, according to the Federal Aviation Administration system status, which showed ground stops requested by United at about 7:30 p.m. ET.

Passenger Angela Jeffers, whose flight from Nashville to Denver was delayed two hours on Wednesday, said the pilot told passengers about the system outage.

“We’re missing some numbers we need to take off so we can’t take off yet and don’t have a time estimate of when we’ll be able to,” she recalled the pilot telling passengers.

She told CNN via text that passengers were given an update around 9:30 p.m. ET that some flights had begun boarding, but due to traffic, not all could. United offered to pay for a hotel and flight for her tomorrow, since her flight hadn’t boarded, Jeffers said.

Her sister Jessica Jeffers was also coincidentally impacted by the disruption Wednesday night, but at a Denver airport. She also told CNN she had been stuck for two hours.

“It’s been pretty rough over here,” Jessica Jeffers told CNN in a text around 9 p.m. ET. “I have been stuck for about two hours on a plane in Denver waiting to go to Newark; with us just now having the option to either deboard or stay on and wait with no direction about what’s going on. The air conditioning has been running really low so we have been essentially baking in here for hours.”

Johan Kotze at Louis Armstrong New Orleans International Airport was also frustrated by the disruptions. He told the Associated Press he was beginning a journey to the Indian Ocean island nation of Mauritius for vacation when he was caught up in the delays, meaning he would likely miss connecting flights along the way and have to rebook flights, a car and accommodation.

“It’s not very nice,” he said of the experience.

This story has been updated with additional information.

NTSB hearing reveals air traffic controllers should have warned plane