Washington DC - Weary travelers braced for more flight disruptions Saturday as service resumed at US airports after an hours-long stoppage that the Trump administration blamed on a botched replacement of old copper wire communication lines.

Friday's nationwide ground stop – meaning no planes could take off – sparked widespread chaos and left hundreds of thousands of passengers in limbo, with some pulled off planes moments before they were due to depart by airline staff who appeared in the dark about unfolding events.

"Tired. Exhausted. Frustrated. Yeah, you know, it's just a mess, right?" Lisa Beraid, 48, who works for an insurance company, told AFP as she waited for a flight Saturday morning at New York's La Guardia airport.

Federal Aviation Administration (FAA) chief Bryan Bedford said that 12,000 flights were canceled on Friday and between four and five thousand flights out of 41,000 scheduled for Saturday were likely to be canceled as well.

Air Travel Trump's transport chief Sean Duffy warns more flights will be canceled after ground stop

By early afternoon, tracking website FlightAware had recorded at least 5,000 canceled flights for Saturday.

Speaking at a news conference in Washington, Bedford offered a "sincere apology to the American traveling public," and predicted a full resumption of flight schedules by "close of business on Sunday."

Transportation Secretary Sean Duffy said Friday's four-hour ground stop was declared after maintenance work to upgrade an old copper wire to a high-speed fiber cable had caused "issues" with communication with airplanes and radar feeds.

"Either through contractor error or a faulty piece of equipment...it started flooding other routers in our air traffic control system," Duffy told reporters.

In another embarrassment, Saturday's news conference – where administration officials also appealed for more funds to upgrade outdated systems – was delayed due to technical problems with the audio feed.

Friday's disruption was only the second time such a ground stoppage had been issued in US airspace – which is among the busiest in the world – since the 9/11 attacks.