The Federal Aviation Administration grounded all flights across the US because of communications problems at regional air traffic control centres.
The FAA notice said the ground stop was being imposed "due to extraordinary circumstances and for reasons of safety".
An Air New Zealand spokesperson said no New Zealand flights have been affected.
Transportation Secretary Sean Duffy said there is a communications issue affecting the 22 regional air traffic control centres that direct planes en route between airports nationwide. He said FAA technicians are investigating.
This is the first nationwide ground stop since January 2023, when a key FAA computer system malfunctioned. Before that the last time had been after the September 11, 2001, attacks.
The government had been working to overhaul the outdated technology that air traffic controllers rely on since Congress approved US$12.5 billion (NZ$22.6 billion) for the project last year. Miles of old copper wires have been replaced with fibre optic lines and old radio systems are gradually being replaced at airports across the country.
But much work remains. Duffy has said that another US$30 billion (NZ$54 billion) will be needed to complete the work, and the White House had begun lobbying Congress to approve it.
The problem appeared similar to a regional air traffic control communication outage in September that snarled hundreds of flights across the Northeast, aviation safety expert Steve Arroyo said, except this time on a nationwide scale. It may be linked to the outdated technology used by air traffic controllers.
"If you don’t have that ability, whether it’s because the old wires that they have are just run down or for whatever reason, you’ve got to stop airplanes on the ground," said Arroyo, who is a former United Airlines pilot.
"And not put them in the air where you’re going to risk not being able to communicate with them."
Saturday's ground stop was different than the one after September 11 because planes were not being told to land immediately and pilots likely were able to communicate with ground controllers at airports, Arroyo said.
More to come
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