Flights across the United States were affected Wednesday morning after the Federal Aviation Administration said it experienced a computer outage.

All flights in the U.S. were grounded following the incident, a source with knowledge of the situation told NBC News.

The FAA said in a notice on its website that its Notice to Air Missions (NOTAM) system had “failed” Wednesday morning. A NOTAM is a notice containing information essential to workers involved in flight operations.

“Technicians are currently working to restore the system and there is no estimate for restoration of service at this time,” it said.

“Operations across the National Airspace System are affected,” the FAA said in a statement to NBC News.

“The FAA is working to restore its Notice to Air Missions System. We are performing final validation checks and repopulating the system now,” it said.

“We will provide frequent updates as we make progress,” it said.

This is a developing story. Please check back for updates.