The Federal Aviation Administration (FAA) issued a nationwide ground stop for all flights in the US on Friday, delaying or canceling more than 11,000 US flights, according to aviation tracker FlightAware, and throwing airports into sudden chaos.

In a post on X, Sean Duffy, the US transportation secretary, said the stoppage is due to “a communication issue impacting all Air Route Traffic Control Centers” and that the FAA’s technicians are looking into the matter.

A notice from the FAA said the ground stop was being imposed “due to extraordinary circumstances and for reasons of safety”.

Markwayne Mullin, the Department of Homeland security director, said in a news conference that preliminary investigations into the stoppage do not indicate that it was tied to a “nefarious attack”.

“There’s no indication as of yet that this was a nefarious attack against it. It’s just a telecommunications outage as of right now,” he told reporters.

After restoring communications so all airborne flights can land, Mullin said, “we’re going to continue to work to find out what the root of the cause is”.

“We’re not ruling out anything at this point,” Mullin added.

Mullin said the immediate priority was ensuring that planes still in the air would be landing safely, but that there was no clear information on how long the stoppage might last.

In a statement, the Los Angeles mayor, Karen Bass, said that she was aware of the stoppage and receiving updates on it. Los Angeles is home to LAX, the fifth-busiest airport in the US, according to the bureau of transportation statistics

“I am in close contact with leadership at Los Angeles World Airports (LAWA) to receive real-time updates and assess impacts. We will continue to monitor this evolving situation and work closely with federal and state partners.”

At Ronald Reagan Washington national airport, gate agents, along with most travelers in the terminal, refreshed their phones looking for updates, and attempted to change their flights. Nearly every seat was filled, with some people sitting on the floor and using their luggage as makeshift desks for their laptops.

On Friday evening, there was still no timeline for when flights will be allowed to resume departures. Amid the continuing confusion at US airports, the California governor, Gavin Newsom, called on the Trump administration to offer more clarity to passengers who are trying to get to their destinations.

“Americans are stuck at airports across the country. They deserve answers, clear updates, and a plan to get home safely. Instead, the Trump Administration is correcting reporters on AI’s “preferred name”. These are not serious people,” Newsom wrote in a post on X, in reference to Mullin correcting a reporter’s use of the term AI earlier in the day.

In an interview on CNN, US congressman Ro Khanna said that he is waiting to be briefed on what exactly led to the technical issues and sparked the ground stoppage and for more public-facing communications from the transportation secretary.

“There’s a lot of nervousness,” Khanna said of the feeling among passengers. “We’re waiting to be briefed in Congress about what, exactly, has happened. We just need communication from them. If they were there every hour briefing the American public, it would help and give us a sense of a timeline.”

According to CNN, the FAA told airlines that the outages are the result of router malfunctions that are believed to have originated at Chicago Midway airport and rippled across the rest of the US.

Amid the uncertainty, San Francisco international airport announced in a social media post that flights bound for Hawaii and Asia were cleared to depart.

John F Kennedy airport posted on its social media that travelers should confirm flight status with the airline before heading to the airport.

British Airways cancelled a flight to New York that had been due to take off from Heathrow at 10.30pm on Friday night, and a spokesperson for Manchester airport confirmed three US-bound flights scheduled to leave on Saturday morning – all operated by Virgin Atlantic – were likely to be affected if the issue was not resolved soon.

A ground-stop order by the FAA requires that aircraft remain on the ground and bars them from taking off. Planes already in the air are usually allowed to remain in the air.

This is the third time all departing flights have been grounded in the US. The first time was on 11 September 2001; the other was in January 2023, when the FAA paused all ⁠domestic departures for less than two hours after a pilot notification system malfunctioned.

The FAA has more than 14,000 air traffic controllers who handle the more than 44,000 flights that take off from airports across the US each day, according to FAA data.

Last week, the FAA announced that the first digital air traffic control towers in the US were officially operational in Alaska and Florida, as part of a modernization project intended to reduce flight delays and improve the flow of air traffic.

Last year, ​Congress ​approved $12.5bn to fix ​the FAA’s ageing communications system, and ​on Friday ‌the FAA ​and ​White House asked Congress for another $30.1bn to address other issues.