A US halt to airplane takeoffs that grounded thousands of flights has been cancelled, the Federal Aviation Administration, the country's national air regulator, said Friday (Nov 13) evening.

All flights in the US were grounded Friday, sparking travel chaos across the vast country, after what government officials said was a major communications outage, insisting it was not the result of any "nefarious attack."

The nationwide stop, lasting more than four hours, left tens 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.

More than 4,700 flights were cancelled and 10,000 delayed on Friday, while another 700 had already been cancelled for Saturday, according to FlightRadar24. Aviation analysts said it could take days for airlines to restore their schedules.

The incident marked only the second time such an alert was given in US airspace since the 9/11 attacks in 2001.

Transportation Secretary Sean Duffy said that US airspace was now "opened up," and blamed "old hardware" for the travel chaos.

Duffy said a legacy air traffic control communications system became overloaded and began issuing faulty data, prompting the nationwide ground stop.

"Our switches, our routers, actually got overloaded with data ... they started to give us inconsistency in the data ... and because of that, we shut the system down," Duffy said at a White House briefing, adding it had intermittent communication and intermittent radar.

Homeland Security Secretary Markwayne Mullin told reporters there was "no cyberattack" and "no connection between this and Microsoft".

Microsoft apologised on Friday for a global outage that began on Thursday and stretched beyond 16 hours, wreaking havoc for millions of users, public services and businesses worldwide

Mullin said there was no sign of a threat to the United States.

"This isn't another 9/11," he said.

"There was no indication, as of yet, that this was a nefarious attack against us, it's just a telecommunication outage, as of right now," Mullin said, adding officials were "not ruling out anything at this point."

In January 2023, the FAA called a nationwide ground stop due to problems with the Notice to Air Missions system (NOTAM), which provides information to pilots about hazards, changes to airport facilities and information that can affect flights. That outage lasted just under two hours.

– with Agencies inputs --