Malvern Group has ceased trading, with as many as 50,000 holidaymakers set to be impacted.
The company operated two firms, Manchester-based Late Rooms and York-based Superbreak Mini Holidays, known as Super Break.
In a statement the company said Super Break hotel-only holidays would be cancelled and people currently on holiday might have to pay again.
The company said it “anticipated” bookings through Late Rooms would be secure.
Late Rooms, acting as an agent, had not taken money for bookings, which would be payable to the accommodation supplier direct, the company said.
Malvern Group said those on package holidays would be protected by ABTA.
The company added its contact centre had closed and it intended to appoint administrators today.
ABTA issued advice for customers of Super Break, but said it did not cover Late Rooms.
In a statement, it said the “vast majority” of Super Break holidaymakers’ arrangements would be covered through ABTA, ATOL or their credit card companies.
“These customers will either be entitled to a refund or, if they have booked through another travel company, they should contact them to discuss options which may include continuing with their booking, re-booking or alternative arrangements,” explained a statement.
Super Break has about 250 employees and had approximately 20,000 bookings, involving about 53,000 people.
About 400 customers are currently on holiday.
Tracey Pye and David Costley-Wood from KPMG Restructuring have been appointed joint administrators to the company.
Pye said: “The directors of Malvern Group embarked upon an accelerated sales process to bring further investment into the business.
“However, with the cash position of the company deteriorating rapidly, this process was unfortunately unsuccessful, prompting the directors to take the difficult decision to appoint the administrators.
“Coming in the midst of the summer holidays, we understand this news will be of grave concern to 23,000 LateRooms.com and 19,000 Super Break customers who have future bookings with the Group.
“We continue to invite offers for the business, and would urge any interested parties to make their interest known as soon as possible.”
With operations ceasing immediately upon the appointment of the joint administrators, the majority of employees have been stood down while the joint administrators assess options for the business.
The joint administrators have retained 43 employees as they continue to seek buyers for the business and its assets.