Flights in the United States have been resuming on Saturday after being grounded for several hours due to a major communications outage, though authorities said returning to normal operations would take time.

The Trump administration boosted its request for air traffic control funding to US$50 billion late on Friday after the communications issue forced a nationwide groundstop that halted thousands of flights.

Transportation Secretary Sean Duffy and the White House had earlier asked for US$30.1 billion to upgrade the United States' aging airports and air traffic control system.

The outage sparked widespread chaos and left hundreds of thousands of passengers in limbo, with some pulled off planes moments before departure by airline staff who appeared in the dark about unfolding events.

The incident marked only the second time such an alert had been issued in US airspace – among the busiest in the world – since the 9/11 attacks.

The ground stop lasted around four hours and was lifted at 8.15pm Eastern Time, or 9.15am on Saturday Hong Kong time.

Federal Aviation Administration officials reopened the airspace on Friday night "after restoring full functionality" at air traffic control facilities, according to Secretary of Transportation Sean Duffy.

"It will take us time [to] resume normal operations... Our top priority is the safety of you and your family when you fly," he said.

Administration officials blamed the incident on telecommunications issues with decades-old equipment, adding there was no evidence of foul play.

"This is a legacy system problem," Duffy said. "We have old, old switches, old routers.

"We use 1980s little copper lines. It's an old system that went down, and went down everywhere. It got overloaded."

As the ground stop was lifted, he repeated his plea.

"I'm going to say it a million times: the Congress has to give the resources to the president so he can finish this bill," he said.

There were almost 6,000 flights canceled, including some international routes, according to FlightAware, a tracking platform.

Homeland Security Secretary Markwayne Mullin stressed there was no evidence of any hostile action on Friday.

"We've seen zero evidence that this was a cyberattack or [AI] attack," he said.

He also ruled out any connection with the outage that affected Microsoft this week, knocking email systems offline for millions of users, public services and businesses worldwide. (AFP)





Edited by Azam Khan