Flights are being delayed at multiple locations across the United States after a computer outage at the Federal Aviation Administration.

Just before 7 a.m. Eastern, there were nearly 1,200 delayed flights within, into or out of the United States, according to the flight tracking website FlightAware.

Most delays were concentrated along the East Coast.

The agency said it was working on restoring its Notice to Air Missions System.

“We are performing final validation checks and reloading the system now,” the FAA said. “Operations across the National Airspace System are affected.”

The agency said that some functions are beginning to come back on line, but that “National Airspace System operations remain limited.”

United Airlines said that it had temporarily delayed all domestic flights and would issue an update once it learned more from the FAA.

The FAA is working to restore what is known as the Notice to Air Missions System.

NOTAMs used to be available through a hotline but that was phased out with the internet. The alerts span from mundane information about construction at airports to urgent flight restrictions or broken equipment.

There is a potential for widespread disruption because of the outage. All aircraft are required to route through the system, including commercial and military flights.

The agency said that it would provide frequent updates as it made progress.