A computer outage has reportedly grounded flights across the US with passengers left stranded at airports. 

The US Federal Aviation Administration’s (FAA) system that alerts pilots and other flight personnel about hazards or any changes to airport facility services and relevant procedures was not processing updated information, the civil aviation regulator’s website showed on Wednesday.

In an advisory, the FAA said its NOTAM (Notice to Air Missions) system had “failed”. There was no immediate estimate for when it would be back, the website showed, though NOTAMs issued before the outage were still viewable.

Over 400 flights were delayed within, into, or out of the United States on Wednesday morning , flight tracking website FlightAware showed. It was not immediately clear if the outage was a factor.

“The FAA is working to restore its Notice to Air Missions System. We are performing final validation checks and reloading the system now,” the FAA said in a statement on Twitter. 

“Operations across the National Airspace System are Affected. We will provide frequent updates as we make progress.” 

A NOTAM is a notice containing information essential to personnel concerned with flight operations, but not known far enough in advance to be publicized by other means.

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