LONDON — Monarch Airlines, a struggling British low-cost carrier and tour operator, collapsed into bankruptcy early Monday, ceasing its flights and forcing the government to step in and bring home more than 100,000 passengers stranded abroad.

Britain’s aviation regulator called the collapse of Monarch the “biggest ever U.K. airline failure.” The airline is one of many that have struggled to grapple with Europe’s highly competitive airline market.

Just this year, the Italian carrier Alitalia went into administration, which is similar to bankruptcy protection in the United States, and is currently seeking a buyer. Air Berlin, a German low-cost carrier, filed for insolvency and has put its assets up for sale.

Ryanair, an Irish discount airline, has expressed interest in making a bid for Alitalia’s assets, but it has faced its own public backlash after it was forced to cancel more than 1,000 flights in September and October because of mistakes in its handling of vacation time for pilots. Last week, Ryanair said it would cancel an additional 18,000 flights on 34 routes between November and March to avoid further cancellations.