United Airlines flights on major routes were grounded Wednesday because of a technology issue, the airline said, and additional flight delays continued into the night.

An alert on the Federal Aviation Administration website said all United flights destined for Chicago were halted at their departing airports. The agency said Denver, Newark, Houston and San Francisco airports were also impacted by halted flights.

“Safety is our top priority, and we’ll work with our customers to get them to their destinations,” an emailed statement from the Chicago based-airline said.

A statement Wednesday night said the underlying technology issue had been resolved and employees were working to restore normal operations.

The impacted system, called Unimatic, houses flight information that is fed to other systems including those that calculate weight and balance and track flight times, according to United.

The system outage, as the company described it, lasted several hours, the statement said. It wasn't related to recent concerns about airline industry cybersecurity.

Benjamin Fuentes told KRTK-TV in Houston that he flew to George Bush Intercontinental Airport from Los Angeles. He said the problems started once the plane was on the ground.

"We had landed and that's when they told us that we were going to be waiting for a while. And we didn't get no further news until maybe an hour into the wait, when they finally told us 'oh, like the whole system's down nationwide. And that's what they told us and they kept telling us. Eventually they said that they had found a gate. But it was like a 45 minute wait until we got to the gate," he said.

Transportation Secretary Sean Duffy said on social media that the issue was unrelated to the broader air traffic control system.