It is only the second time flights have been grounded in the US since the September 11, 2001, terror attacks. ( Reuters: Joshua Lott )
Flights in the United States have resumed after the US Federal Aviation Administration earlier issued a national ground stop due to safety.
It was only the second time flights have been grounded in the US since the September 11 terror attacks in 2001.
The grounding had been called due to a communication issue affecting 22 regional air traffic control centres.
The US Federal Aviation Administration (FAA) says flights can now resume, after it earlier issued a national ground stop "due to extraordinary circumstance and reasons for safety".
US Transportation Secretary Sean Duffy confirmed the ground stop was due to a communication issue affecting all air route traffic control centres.
Mr Duffy said there was a communications issue affecting 22 regional air traffic control centres that direct planes en route between airports nationwide.
He said FAA technicians were investigating the cause of the issue.
US Homeland Security Secretary Markwayne Mullin said there was no indication yet of a nefarious act behind the communication issue.
"It's just a telecommunications outage … everybody's safe. There's no reason to be concerned about your loved ones if they're flying."
Mr Mullin said investigators would look at whether there was any link to the FAA's nationwide rollout of a new artificial intelligence system to help identify problems and reroute planes.
But the system operates out of one location near Washington DC, and only sends recommendations to the air traffic control centres.
Shortly before the announcement, the FAA halted traffic in Chicago due to air traffic control issues.
The agency said: "All departing traffic should remain ground stopped until further notice."
The FAA said international flights would be managed on a case-by-case basis.
According to the Eurocontrol website, all US-bound traffic from its member states were suspended at the FAA's request because of technical issues.
There are 42 Eurocontrol member states, including Israel.
FlightAware, an online aircraft-tracking website, is reporting that about 10,500 flights in and out of the US have already been delayed today.
The website also said more than 1,800 flight services had been cancelled.
Traveller Jeff Dubner was still waiting to disembark from his plane an hour and a half after leaving the gate at Los Angeles International Airport.
"It's frustrating. This certainly sounds like it's going to be more than the usual run-of-the-mill delay. I look forward to finding out why," he said.
This is only the second nationwide ground stop in the US since the September 11 terror attacks in 2001.
The last one was in January 2023, when domestic departures were paused for less than two hours.
