The US Federal Aviation Administration has grounded all departing flights nationwide after a communications failure hit air traffic control centres across the country.
The FAA cited "extraordinary circumstance and reasons for safety" for the groundstop.
The announcement means planes in the air may land, but those on the ground cannot take off.
The Homeland Security secretary Markwayne Mullin says there is no indication yet of any nefarious act behind the FAA communications issue.
Flight tracking service FlightAware said nearly 7,000 flights were delayed or cancelled due to the nationwide ground stop.
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"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. We will provide immediate updates as we have them," Transportation Secretary Sean Duffy said.
The disruption is the latest sign of strain on the US air traffic control system, which has been beset by equipment failures, communications problems and shortages of controllers while the FAA tries to replace aging infrastructure.
Congress approved $12.5 billion for the overhaul last year, and the FAA and White House asked lawmakers on Friday for another $30.1 billion.
Shortly before the announcement, the FAA halted traffic in Chicago due to air traffic control communications issues. The agency said, "all departing traffic should remain groundstopped until further notice." The FAA said it would manage international flights on a case-by-case basis.
Saturday's halt was the second nationwide ground stop of all departures since the September 11 attacks. The other happened in January 2023, when the FAA paused all domestic departures for less than two hours.
