NEW YORK A Federal Aviation Administration (FAA) system failure has caused flights across the United States to be grounded, leading to delays at airports.

The full extent of the delays was not immediately known, and some flights managed to take off, but the delays were spread across several airlines.

More than 1,200 flights within, into and out of the US were delayed on Wednesday, and at least 100 were cancelled, according to FlightAware, a flight tracking company.

United Airlines said in a statement it temporarily delayed all domestic flights and that it would issue an update when it learned more from the FAA.

The FAA said it ordered airlines to pause all domestic departures until 9am ET (10pm in Singapore) to allow it to validate the integrity of flight and safety information.

Germanys Lufthansa and Air France both said they were continuing to operate flights to and from the US, as they tracked progress reports and advisories coming from the FAA.

Arriving and departing passengers can expect delays this morning and throughout the day, Austin-Bergstrom International Airport said on Twitter, adding that there had been ground stops across the US.

A ground stop is an air traffic control measure that slows or halts aircraft at a given airport.

The operator of Paris international airports said it was expecting flight delays due to the FAA system outage.

We have been informed of a technical incident. At this stage, there have been no flight cancellations but some delays are to be expected, a spokesman for Aeroports de Paris (ADP) said.

ADP operates Paris Charles de Gaulle and Orly airports.

The FAA said it was working to restore a system that alerts pilots to hazards and changes to airport facilities and procedures that stopped processing updated information.

It said it was still working to fully restore the Notice to Air Missions (NOTAM) system following an outage.

While some functions are beginning to come back on line, National Airspace System operations remain limited, it said on Twitter. Embed Twitter Tweet URL A NOTAM is a notice containing information essential to personnel concerned with flight operations, but not known far enough in advance to be publicised by other means.

Information can go up to 200 pages for long-haul international flights and may include items such as runway closures, bird hazard warnings and construction obstacles.

The new disruptions follow closely on a December operations meltdown at Southwest Airlines that forced the carrier to cancel more than 16,700 flights and drove the airline to a fourth-quarter loss.

A total of 21,464 flights are scheduled to depart airports in the US on Wednesday with a carrying capacity of nearly 2.9 million passengers, data from Cirium shows.

American Airlines has the most departures from US airports with 4,819 flights scheduled, followed by Delta Air Lines and Southwest. REUTERS, NYTIMES More On This Topic Manila airport scrambles to restore normality after power cut; about 65,000 passengers affected 'Travel insanity': US passengers stranded by winter storm