Departures from all US airports have been suspended - the country's Federal Aviation Administration made the decision. This is reported in the news.
The restrictions took effect at 15:53 local time. Preliminary indications are that they are set to last until 23:00-23:30.
US Transportation Secretary Sean Duffy clarified that the reason for these measures was a communications failure in air traffic control centers.
According to the Flightradar24 service, about 3,100 aircraft heading to US airports are currently in the air.