The Federal Aviation Administration late Friday afternoon issued a nationwide "ground stop," affecting flights across the country.

US Transportation Secretary Sean Duffy said just after 4:15 pm. Eastern time that the nationwide flight traffic halt came "following a communication issue impacting all Air Route Traffic Control Centers."

"FAA technicians are investigating the issue," he said in a post on X. "We will provide immediate updates as we have them."

The agency said the stop was due to "extraordinary circumstances and for reasons of safety."

As of late Friday afternoon, delays were already piling up at airports across the country, according to the FAA's monitoring system: At Newark Liberty International Airport in New Jersey, outside of New York City, the average delay was more than 45 minutes. It was the same at the Houston-Bush Intercontinental Airport — and even worse at Chicago O'Hare, where delays were 75 minutes and rising.

The FAA notice said that inbound international flights would be managed on a "case-by-case basis."

"The FAA issued a nationwide ground stop for all US airports following communication issues impacting multiple Air Route Traffic Control Centers," an FAA spokesperson told Business Insider. "FAA technicians are investigating the issue. We will provide updates."

This is a developing story. Check back for updates.