The US Federal Aviation Administration has issued a national ground stop "due to extraordinary circumstance and reasons for safety" after the agency earlier reported serious air traffic control communications issues.
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 will be managed on a case-by-case basis.
The US Transportation Secretary Sean Duffy confirmed it was due to a communication issue affecting all air route traffic control centres.
Mr Duffy said FAA technicians were investigating the issue.
