All flights departing the US have been grounded by the US Federal Aviation Administration “due to extraordinary circumstance and reasons for safety”.

The FAA ordered the national ground stop shortly after it halted traffic in Chicago due to air traffic control communications issues.

“All departing traffic should remain ground stopped until further notice,” the agency said.

The announcement means planes in the air may land, but aricrafts on the ground cannot take off.

Flight tracking service FlightAware said nearly 7,000 flights were delayed or cancelled due to the nationwide ground stop.

Transportation Secretary Sean Duffy said the incident, believed to be caused by a “communication issue”, was being investigated.

“The FAA issued a nationwide ground stop for all US airports following a communication issue impacting all Air Route Traffic Control Centres. FAA technicians are investigating the issue,” he said.

“We will provide immediate updates as we have them.”

Meanwhile, US Homeland Security Secretary Markwayne Mullin reassured passengers were not in danger as there was so far no indication of a nefarious act.

“We had no reason to believe that — as of right now, that this was a threat to the United States,” he told reporters in Washington.

“It’s just a telecommunications outage … everybody’s safe. There’s no reason to be concerned about your loved ones if they’re flying.”

When asked if the incident could have been caused by a cyber attack, Mr Mullin said this isn’t “another 9/11” adding that officials would not yet rule out any potential causes.

Back on Australian soil, travellers heading to the US are being urged to check their flight details as the rare aviation warning causes chaos.

Sydney Airport said its operations had not been affected by the FAA order, but urged travellers to look out for updates from their airline.

“We are aware of the nationwide ground stop issued by the US Federal Aviation Administration and are monitoring the situation closely,” a spokesperson said in a statement.

“At this stage, there is no impact to operations at Sydney Airport.

“Passengers travelling to or via the United States should check with their airline for the latest information regarding their flight.”

Qantas issued similar advice to its passengers, saying the outage was yet to affect its operations.

Friday’s halt was the second nationwide ground stop of all departures since the September 11, 2001, attacks. The other happened in January 2023, when the FAA paused all domestic departures for less than two hours.

with NCA Newswire