Longtime British tour company Thomas Cook has taken its last trip, leaving thousands stranded.
The company collapsed after failing to secure rescue funding, and travel bookings for its more than 600,000 global vacationers were canceled early Monday.
The British government said the return of the firm's 150,000 British customers now abroad would be the largest repatriation in its peacetime history.
The process is set to begin later Monday and officials warned that delays are inevitable.
The Civil Aviation Authority said Thomas Cook has ceased trading, its four airlines will be grounded.
The company's 21,000 employees in 16 countries will lose their jobs.
The company several months ago had blamed a slowdown in bookings because of Brexit uncertainty for contributing to its crushing debt burden.
The 178-year-old company had said Friday it was seeking 200 million pounds ($250 million) to avoid going bust and was in weekend talks with shareholders and creditors to stave off failure. The prominent firm, whose airliners were a familiar sight in many parts of the world, also operated around 600 UK travel stores.
The company's chief executive Peter Fankhauser said, "This marks a deeply sad day for the company which pioneered package holidays and made travel possible for millions of people around the world."
He said a deal had been "largely agreed" but that "an additional facility" requested in the last few days presented an insurmountable challenge but provided no further details.
"I would like to apologize to our millions of customers, and thousands of employees," he said in a statement.
Describing the repatriation plan, British Transport Secretary Grant Shapps said dozens of charter planes, from as far afield as Malaysia, had been hired to fly customers home free of charge. He said hundreds of people were staffing call centers and airport operations centers.
Unions representing the Thomas Cook staff had urged the British government to intervene to prop up Thomas Cook.
Most of Thomas Cook's British customers are protected by the government-run travel insurance program, which makes sure vacationers can get home if a British-based tour operator fails while they are abroad.
Thomas Cook, which began in 1841 with a one-day train excursion in England and now operates in 16 countries, has been struggling over the past few years. It only recently raised 900 million pounds ($1.12 billion), including receiving money from leading Chinese shareholder Fosun.
An estimated 1 million future travelers will find their bookings for upcoming holidays cancelled. They are likely to receive refunds under the terms of the government's travel insurance plan.
The Associated Press contributed to this article.