Despite the reopening of airspace and the resumption of flight departures, airlines struggled to restore their normal operating schedules.
Major airports in Dallas, Houston, Chicago, Atlanta and New York experienced widespread disruption, with passengers facing lengthy waits and missed connections.
According to FlightAware data, a total of 6,228 flights arriving in and departing from the United States were cancelled, while another 7,542 flights were delayed.
The figures exceeded an earlier forecast by Federal Aviation Administration (FAA) chief Brian Bedford, who had estimated that between 4,000 and 5,000 of the day's approximately 41,000 scheduled flights could be cancelled.
Worldwide, 6,843 flights were cancelled and 19,927 delayed, with a significant proportion of the disruptions involving US-related flights.
JetBlue was among the worst-affected major airlines, cancelling approximately 45 per cent of its scheduled flights. American Airlines, United Airlines and Delta Air Lines also cancelled around a quarter of their scheduled services.
RELATED: US Resumes Flights After Air Traffic Network Failure Chaos
Airlines have announced that affected passengers will be allowed to rebook their journeys for alternative dates without additional charges.
Chicago's O'Hare International Airport was among the hardest-hit airports, recording more than 559 cancellations by 2pm. Chicago Midway Airport also reported 68 cancelled flights.
At Hartsfield-Jackson Atlanta International Airport, a major hub for Delta Air Lines, 479 flights had been cancelled by 12:30pm.
In Texas, Dallas-Fort Worth International Airport recorded approximately 300 cancellations by 9am. Several passengers were forced to spend the night at the airport, while travellers with connecting flights faced particularly difficult circumstances.
Houston's George Bush Intercontinental Airport reported more than 310 cancellations by the evening, while disruptions and delays also continued at William P. Hobby Airport.
The US Department of Transportation said that airspace remained open and flights were operating safely. However, passengers were advised to prepare for further cancellations and delays as airlines worked to reposition aircraft and crew members and arrange alternative travel for affected customers.
READ MORE: Upgrade Work Blamed for Nationwide Flight Shutdown
Airlines are facing significant operational challenges in returning aircraft and staff to their scheduled airports and clearing the backlog of disrupted journeys.
Officials expressed hope that airlines would restore their full operating schedules by Sunday night, although passengers were advised to remain alert for further changes to their travel plans.