The United States Federal Aviation Authority said on Wednesday it was "working to restore" a key flight information system, with flight operations across the country affected.

The United States Federal Aviation Authority ordered domestic departures paused until 9:00 am EST (1400 GMT) on Wednesday after a system outage halted flight operations across the country.

"The FAA is still working to fully restore the Notice to Air Missions system following an outage," the agency said in a statement, adding that while "some functions are beginning to come back on line, National Airspace System operations remain limited."

There is no sign of a cyberattack "at this point" in the computer problem that triggered US authorities to pause all domestic air travel departures Wednesday, the White House said, adding that President Joe Biden has been briefed.

The NOTAM system provides information to flight crews about hazards, changes to airport facilities and other essential information on procedures. The FAA said the processing of NOTAMs was "impaired".

Major US carrier United Airlines said shortly after the announcement it had "temporarily delayed all domestic flights" due to the outage.

There were at least 1,230 flights delayed in the United States by 7:00 am US Eastern time (1200 GMT), flight tracking website Flight Aware data showed, although it was unclear how many of those delays were related to the outage.

US Transportation Secretary Pete Buttigieg said he was in contact with the FAA.

"I have been in touch with FAA this morning about an outage affecting a key system for providing safety information to pilots," he tweeted.

"FAA is working to resolve this issue swiftly and safely so that air traffic can resume normal operations, and will continue to provide updates."