At least 285,000 people have been hit in the biggest holiday operator failure for more than two decades.
A total of 85,000 people who booked holidays or flights through XL Leisure Group are thought to have been affected immediately after Britain's third largest tour operator went into administration.
It is estimated there are 50,000 customers abroad who had booked through an XL tour operator, 10,000 on holiday with XL Airways, and 25,000 with other tour operators who shared the XL flights.
A further 200,000 customers have advance bookings.
The company, which blamed the move on volatile fuel prices and the economic downturn, had also left its own staff "in the dark" over its plight.
All XL Airways flights have been cancelled and customers advised not to go to the airport.
The collapse of the company, which operated out of a dozen airports in the UK, has affected flights across the country.
Seven flights due to land at Gatwick have been cancelled, as have seven that would have arrived at Manchester airport. XL flights in Glasgow and Newcastle airports have also been affected by collapse.
Travellers at Manchester airport were greeted with a three-page A4 photocopy announcing the news.
People who booked package holidays through The Really Great Holiday Company, Kosmar Holidays, Freedom Flights, and Aspire Holidays are protected under the Air Travel Organiser's Licenses (ATOL) scheme.
They will be able to complete their holiday if they are already abroad and a flight will be arranged by the Civil Aviation Authority to bring them home.
Anyone who has booked a holiday with one of the four companies but has not left yet has been advised to contact their travel agent to make a claim.
But it is estimated that more than 10,000 people are not ATOL protected because they booked separate flights and accommodation or flights only.
The CAA will be able to make arrangements for stranded holidaymakers to fly home - but they are not eligible for refunds.
Thomson and First Choice have said they will step in to help those on ATOL protected flights or holidays.
XL Airways, which provided flights to more than 50 destinations in Europe, Africa and America.
XL Collapse: Who To Call For Help
A total of 85,000 people who booked holidays or flights through XL Leisure Group are thought to have been affected immediately after Britain's third largest tour operator went into administration.
It is estimated there are 50,000 customers abroad who had booked through an XL tour operator, 10,000 on holiday with XL Airways, and 25,000 with other tour operators who shared the XL flights.
A further 200,000 customers have advance bookings.
The company, which blamed the move on volatile fuel prices and the economic downturn, had also left its own staff "in the dark" over its plight.
All XL Airways flights have been cancelled and customers advised not to go to the airport.
The collapse of the company, which operated out of a dozen airports in the UK, has affected flights across the country.
Seven flights due to land at Gatwick have been cancelled, as have seven that would have arrived at Manchester airport. XL flights in Glasgow and Newcastle airports have also been affected by collapse.
Travellers at Manchester airport were greeted with a three-page A4 photocopy announcing the news.
People who booked package holidays through The Really Great Holiday Company, Kosmar Holidays, Freedom Flights, and Aspire Holidays are protected under the Air Travel Organiser's Licenses (ATOL) scheme.
They will be able to complete their holiday if they are already abroad and a flight will be arranged by the Civil Aviation Authority to bring them home.
Anyone who has booked a holiday with one of the four companies but has not left yet has been advised to contact their travel agent to make a claim.
But it is estimated that more than 10,000 people are not ATOL protected because they booked separate flights and accommodation or flights only.
The CAA will be able to make arrangements for stranded holidaymakers to fly home - but they are not eligible for refunds.
Thomson and First Choice have said they will step in to help those on ATOL protected flights or holidays.
XL Airways, which provided flights to more than 50 destinations in Europe, Africa and America.
XL Collapse: Who To Call For Help