LONDON — Hundreds of thousands of vacationers were left stranded when one of the world’s oldest tour companies, Thomas Cook, abruptly announced Monday, with some of its flights still in the air, that it was going out of business.

Amid scenes of confusion at European airports, British officials scrambled to bring home 150,000 travelers, chartering dozens of jets to bring people home from as far away as Malaysia. It was described as the largest peacetime repatriation effort in the country’s history.

The tour company, said that all its bookings, including flights operated directly by the agency, had been canceled. “We are sorry to announce that Thomas Cook has ceased trading with immediate effect,” it said.

With that, travel plans for hundreds of thousands were snarled, and tourism officials in vacation hot spots braced for a potentially devastating hit to their economies.