Thomas Cook is set to go into administration, according to ITV News sources, leaving around 9,000 jobs hanging in the balance.
It comes after bosses had spent the day trying to secure £200 million to keep the travel business going - but may ultimately have failed.
ITV News Business and Economics Editor Joel Hills has said the announcement, which is expected early Monday morning, will trigger Project Matterhorn - the government's plan to repatriate 150,000 holidaymakers stranded abroad.
Earlier on Sunday, the world's oldest travel operator met with the firm’s biggest shareholder along with creditors in a final bid to piece together a rescue deal.
As he left the meeting, Chief Executive Dr Peter Fankhauser did not comment on what had been discussed.
The travel operator's boss walked out of the service exit of law firm Latham & Watkins, in Bishopsgate, central London, surrounded by colleagues after the meeting ran from 9am until shortly before 5.30pm.
Dr Fankhauser did not answer questions when he was asked whether Thomas Cook and their creditors had reached a deal.
Cabin crew team member Emily Rose shared a photo on social media of crew and passengers on possibly one of the last Thomas Cook flights leaving on holiday on Sunday night.
Dominic Raab earlier assured the firm’s worried customers contingency planning is in place in the event the business cannot be saved.
The foreign secretary told the BBC’s Andrew Marr Show that the Government had "got all the contingency planning to make sure no one will be stranded."
He said: "I don’t want to give all the details of it because it depends on the nature of how people are out there, whether they have got a package holiday or whether they just paid for the flights and sorted out something separately."
He added: "But I can reassure people that in the worst case scenario, the contingency planning is there to avoid people being stranded."
Brian Strutton, general secretary of the British Airline Pilots Association, said: "Thomas Cook staff are going through hell as their livelihoods are put on the line, they have no idea if they will wake up tomorrow with a job or not.
"Their dignity in carrying on working for Thomas Cook customers under this pressure is a credit to them."