The UK Civil Aviation Authority (CAA) made the announcement the company had gone into administration and urged those with booked Flybe flights not to travel to airports.
Three early Flybe flights from Belfast, two from Birmingham and two from Amsterdam were all showing as 'scheduled on time' on Flybe's online flight status live tracker at 5am.
But the CAA urged ticket-holders to instead check its website for the latest information.
CAA consumer director Paul Smith said: "It is always sad to see an airline enter administration and we know that Flybe's decision to stop trading will be distressing for all of its employees and customers.
"We urge passengers planning to fly with this airline not to go to the airport as all Flybe flights are cancelled. For the latest advice, Flybe customers should visit the Civil Aviation Authority's website or our Twitter feed for more information."
The airline also confirmed the "sad" move, noting that administrators had been brought in.
"We are sad to announce that Flybe has been placed into administration," Flybe tweeted.
"David Pike and Mike Pink of Interpath have been appointed administrators. Flybe has now ceased trading. All Flybe flights from and to the UK are cancelled and will not be rescheduled."
It comes after Flybe returned to the skies in April following an earlier collapse.
It returned with a plan to operate up to 530 flights per week across 23 routes, serving airports such as Belfast City, Birmingham, East Midlands, Glasgow, Heathrow and Leeds Bradford.
Flybe was pushed into administration in March 2020 with the loss of 2,400 jobs as the Covid-19 pandemic destroyed large parts of the travel market.
Before it went bust it flew the most UK domestic routes between airports outside London.
Its business and assets were purchased in April 2021 by Thyme Opco, which is linked to US hedge fund Cyrus Capital.
Thyme Opco was renamed Flybe Limited.
It had been based at Birmingham Airport.
The Government said that its "immediate priority" would be to support anyone trying to get home and those who have lost their jobs.
"This remains a challenging environment for airlines, both old and new, as they recover from the pandemic, and we understand the impact this will have on Flybe's passengers and staff.
"Our immediate priority is to support people travelling home and employees who have lost their jobs," a spokesperson said.
"The Civil Aviation Authority is providing advice to passengers to help them make their journeys as smoothly and affordably as possible.
"The majority of destinations served by Flybe are within the UK with alternative transport arrangements available.
"We recognise that this is an uncertain time for affected employees and their families.
"Jobcentre Plus, through its Rapid Response Service, stands ready to support any employee affected."
Matthew Hall, chief executive of Belfast City Airport, said: "First and foremost, our thoughts are with Flybe employees and passengers affected by this disappointing and unexpected news.
"Passengers booked on Flybe flights should not travel to the airport and should seek further advice from the Civil Aviation Authority.
"Flybe operated 10 flights to and from Belfast City, eight of which are currently served by other carriers from our airport."