Chicago, Illinois - Thousands of air passengers were facing delays Wednesday after United Airlines halted many departures in the wake of a systemwide problem.

So-called "mainline flights" – those moving between major hubs – were grounded for over an hour before engineers were able to get things up and running again.

"We are working with customers to get them to their destinations after a technology disruption on Wednesday evening," the airline said in a statement.

"The underlying technology issue has been resolved, and, while we expect residual delays, our team is working to restore our normal operations."

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The Federal Aviation Administration, which regulates flight in the US, had issued ground stops at several major airports.

"We're aware United experienced a technology issue disrupting their operations. Some delays may continue as they work through the recovery process," the FAA said in a statement.

"We've offered full support to help address their flight backlog and remain in close contact with United."

The orders affected airports in Denver, Newark, Houston, and Chicago and only applied to United, the FAA's website said.

The outage was the latest problem to afflict America's aviation sector.

Last month, Alaska Airlines suffered an IT problem that left its planes on the ground for several hours.

That came after air traffic control systems went down at a Newark area airport on more than one occasion this year, shaking passengers' faith in the system.

In January, a mid-air collision near Washington's Reagan National Airport involving a passenger jet and a military helicopter claimed dozens of lives.