By Agence France-Presse
"This is the biggest ever UK airline failure," the airlines regulator said on Twitter as it announced that Monarch and its holiday company had ceased operations.
The British government had asked the CAA to help repatriate the stranded passengers and it said it was securing more than 30 aircraft to bring them back home.
"Monarch customers in the UK: don't go to the airport. There will be no more Monarch flights," the budget carrier said on Twitter.
The airline had been struggling financially and won a cash injection last October allowing it to continue flying holidaymakers and fund growth plans, as the sector faced turbulence from Brexit and terrorism.
Majority shareholder Greybull Capital had pumped another 165 million pounds ($220 million, 185 million euros) into Monarch to allow the airline to retain its licence to carry on selling package holidays.
Extension of the group's Air Travel Organiser's Licence (ATOL) membership -- a scheme which is funded by the sector and compensates travellers in the case of a company collapse -- had been on condition of fresh funding.
The CAA had renewed Monarch's ATOL licences until the end of September 2017.
Monarch, based at Luton airport north of London, had been due to take delivery of the first of 30 Boeing 737 MAX-8 aircraft in 2018.