A major malfunction in the system that routes planes through 160,000 square miles of airspace centered over Washington caused airlines to delay or cancel hundreds of flights nationwide Saturday, and some frustrated passengers won’t reach their destinations until Sunday.

The Federal Aviation Administration said it was not immediately able to determine what caused the problem.

“The FAA is continuing its root cause analysis to determine what caused the problem and is working closely with the airlines to minimize impacts to travelers,” the FAA said in a statement.

Two airports serving the Washington region were particularly hard hit, with dozens of outbound flights canceled or delayed. Airports in the New York area also had delays, and scores of flights headed to Reagan National Airport and Baltimore-Washington International Marshall Airport also were canceled, stranding passengers overnight at airports across the nation.

“Are we wasting our time being here?” Laurence Oster, 40, said as he sat at BWI with his wife and two young sons, wondering whether their flight to Manchester, N.H., would get off the ground. “You would think it’s a Saturday” — he snapped his fingers — “it would be a breeze.”

It wasn’t. Their flight was canceled.

Many passengers complained that authorities had left them in the dark, noting that the FAA posted no information about the problem on Twitter until 4:30 p.m. — after it had been fixed.

“The airline was saying, ‘It’s not our fault, it’s the airport,’ and the airport said, ‘It’s not our fault, it’s the FAA,’ but you go to their Twitter account and they [FAA officials] haven’t said anything about it,” said Ilya Lozovsky, 32, who had been waiting for more than seven hours at Dulles International Airport for his flight to Alaska for a long-awaited vacation.

Although the malfunction caused delays and cancellations up and down the Eastern ­Seaboard, the problem was ­confined to the Washington air-traffic control center in Leesburg, Va. For several hours, the system that processes flight plans at the center stopped functioning for reasons that are still unclear. Federal authorities said there was no indication that hackers had breached the system.

The FAA said that the system had been restored to service by 4 p.m., but it is ultimately up to airlines to sort out the mayhem caused to their scheduling.

The Washington facility and other control centers dictate routing once airplanes reach an altitude above about 20,000 feet. (Once they go below that altitude, they are directed to airports by controllers at Terminal Radar Approach Control Facilities called TRACONs. For final approaches and takeoffs, they are directed from control towers.)

When the Washington control center stopped functioning, the TRACON serving National and BWI had no one it could hand flights off to as the planes reached cruising altitude. And East Coast flights — for example, a Miami-New York flight — were delayed or routed around the airspace controlled by the Washington center.

After standing in line with for an hour and a half, Alisha Lalani, 10, of Fort Lauderdale, Fla., looks at her phone as her mother and brother check in for their flight to Miami at Washington’s Reagan National Airport. (Jacquelyn Martin/AP)

The disruption, which some on social media dubbed “flypocalypse,” infuriated travelers who can usually count on the system to function on schedule on a Saturday, when thunderstorms are generally the only variable that causes delays or cancellations. Their frustration was exacerbated because the airlines first had no knowledge of what was causing the delays and then weren’t able to say when — or if — their flights might be able to take off.

The words “canceled” and “delayed” taunted travelers from departure boards at airports, keeping them from joining family reunions, shipping off to college and heading home from vacation.

“It’s been a long day, and it’s still going on,” said Magdalena Ruiz, who woke up at 4 a.m. in London to head back to West Virginia via Dulles. “It’s really killing us.”

Dulles was the least affected of the three big Washington-area airports. By early evening, although there were 154 inbound and outbound flights delayed there, only 5 percent had been canceled. By contrast, about 25 percent of inbound and outbound flights were canceled at National and BWI.

The FAA worked with airlines to keep some flights in and out of the region’s airports in operation. It achieved that by keeping the flights below 20,000 feet and having TRACON controllers hand off directly to another TRACON rather than to the Washington control center.

“I’m doubtful it’s actually going to get out,” Gabriella Stefano, 19, said as she stared at a monitor in Terminal B at BWI, hoping to learn whether a flight scheduled for 6 p.m. would get her to Atlanta.

She and her mother said they booked an additional flight to Atlanta at 6 a.m. Sunday in case Saturday’s flight was canceled. The Clemson University sophomore needed to make it back to school in South Carolina before classes start Wednesday.

If both flights fell through, “we’re just going to drive the nine hours,” she said. “I mean, what can you do?”

Leslie Aun of Arlington, Va., was stuck on a plane in Chicago for two hours, trying to get home after a trip to Montana.

“Delayed, delayed, delayed,” Aun said. “I thought, ‘Oh my gosh — am I ever going to get home?’ ”

Aun said it wasn’t clear what was happening until about an hour into the delay.

“The gate guy finally stood up and really talked to us and told us about what happened,” Aun said. “My sense was that the airlines weren’t entirely sure. They were calling the pilots and asking the pilots for updates. Pilots were calling the air-traffic controllers.”

Sharon Fisher’s 11:15 a.m. flight to Grand Rapids, Mich., had boarded at BWI and was leaving the gate when a cancellation announcement came from the cockpit, she said.

“I think if we had left five minutes beforehand, it would have been okay,” she said.

Fisher, 64, rescheduled her Southwest flight for 9:25 p.m. Saturday. Instead of landing in Grand Rapids, she said, she is flying to Detroit, where a friend has offered to pick her up and drive her the rest of the way.

“I just kind of roll with the punches,” she said.

Brian Norment reported that his plane sat waiting to take off in Fort Walton, Fla., for two hours before he was told that the earliest flight he could take back to National wouldn’t be until Monday morning. He said he planned to make the 14-hour drive back to the D.C. area instead.

Anya Shah grilled a Southwest Airlines representative at National on Saturday afternoon while waiting in line to rebook her canceled flight to Nashville.

“I’m fired if I don’t get there by 10 o’clock tomorrow,” she told the agent. She received sympathy but no guarantees. Flights had already been almost fully booked before Saturday’s delays, and with so many flights canceled, it wasn’t a sure thing that she could get on a later flight.

Shah stayed in a rebooking line and kept trying to call reservation phone lines, but a recording told her that there was a 60-minute wait for a call back.

At BWI, as a Southwest flight bound for Nashville boarded, the gate agent thanked the passengers for their patience. As he began to close the door after a seven-hour delay, they applauded.

Amy Ellis Nutt, Dan Balz, Will Greenberg, Anne Kenderdine, Elizabeth Koh and Patricia Sullivan contributed to this report.