Liz Dover Baker, head of school at The GreenMount School in Baltimore, was walking her dog about 6 a.m. Thursday when her phone began lighting up with frantic calls, emails and messages.

A group of 13 students and three teachers from the independent school in Remington had planned to fly Friday evening to Reykjavik, Iceland, from BWI Thurgood Marshall Airport for the eighth-grade “Immersion Experience,” which they would spend touring the world’s northernmost capital city and exploring a farm in the countryside.

But WOW Air, the Icelandic budget airline they’d bought tickets for, announced Thursday morning it would cease all operations, stranding passengers across two continents — and leaving GreenMount parents and school officials calling other airlines, scrambling to salvage the trip.

“It’s just really disappointing,” Baker said.

“The good news is, while we book these trips privately, we always purchase insurance. We’ll get our money or some portion of our money back. Parents and teachers are on laptops right now, booking what they can.”

Launched by Icelandic entrepreneur Skúli Mogensen in 2012, WOW Air offered ultra-low-cost flights between the United States and Europe, starting at $99 and connecting through Reykjavik.

The airline selected Baltimore/Washington International as one of its first North American hubs in 2014, and the new route received so much interest that WOW began offering the service a month early and made it year-round instead of seasonal.

Often the cheapest trans-Atlantic option for U.S. passengers willing to deal with a layover, the airline flew beyond Reykjavik to 20 European cities. It offered year-round service to London, Berlin, Copenhagen, Paris, Dublin and Amsterdam.

In a statement on its website Thursday, the airline, which had earlier suspended all its flights, told passengers there would be no further flights and advised them to check flights with other airlines for ways to reach their destinations.

The airline’s bankruptcy comes after six months of turbulent negotiations to sell the low-cost carrier, first to its main rival and national flagship carrier Icelandair and later to Indigo Partners, an American company operating the airline Wizz Air.

"I will never forgive myself for not acting sooner," Mogensen said in a letter to employees Thursday. "WOW was clearly an incredible airline and we were on the path to do amazing things again."

Rita Walters, who lives in Roland Park, arrived back at BWI Marshall on one of the last WOW Air flights at 6 p.m. Wednesday, after an eight-day trip to Paris.

Walters, 54, the chief development officer for Catholic Charities, had flown with the airline a handful of times since it debuted service to BWI, including with her family to spend Thanksgiving with her son in London in 2016.

“My heart goes out to my fellow budget-ballers who are probably stuck, who knows where,” she said. “[WOW Air’s] whole model was to have you stay over in Reykjavik and have you spend money in the capital.”

Refunds to those with canceled flights likely won’t do much good for stranded passengers, Walters said, because the next cheapest flights are far more expensive than WOW Air’s ultra-low-cost fares.

“Here’s a dollar back, because the flights are so cheap,” she said. “Come up with another $5,999 to get on Air France. It’s ridiculous.”

Dana Legg, 22, of Pasadena, had a $770 WOW Air trip booked from Newark, N.J., through Reykjavik to Berlin with her boyfriend for his cousin’s wedding in August. Her boyfriend is the best man.

Relatives have been lighthearted about the situation, said Legg, who works in public affairs at the Naval Academy.

One sent a picture of Aladdin and joked they might need a flying carpet to get to the wedding, which is taking place in Poland.

“It’s a stressful situation all around,” she said. “It’s not terribly inconvenient, but I hope it gets sorted out soon, because tickets are only going to get more expensive the longer we wait.”

Tourism is Iceland's largest industry and WOW's disappearance is set to have an effect on this summer's high season.

In its early years, the airline expanded quickly to 37 destinations and reported up to 60 percent annual growth in passenger numbers.

Its revenue per passenger, however, has not kept up and fell by about 20 percent in 2017, according to the last earnings report.

WOW grounded at least six planes in North America that were set to leave late Wednesday from Montreal, Toronto, Boston, Detroit and New York, as well as Baltimore.

In Europe, Reykjavik-bound planes from seven cities — Amsterdam, Dublin, Paris, Brussels, Berlin, Frankfurt and Copenhagen — did not take off Thursday morning.

The Associated Press contributed to this article.