Passengers were told not to turn up for flights after the airline they had booked with collapsed.
Flybe warned passengers in the early hours of Saturday that the airline was in administration.
The airline had gone into administration previously, in March 2020, but was able to resume flights.
Flybe passengers were told overnight not to turn up for flights after the airline collapsed for the second time in less than three years.
A notice posted on Flybe's website said the airline was no longer trading.
"Flybe has now ceased trading and all flights from and to the UK operated by Flybe have been canceled and will not be rescheduled," the notice said. "If you are due to fly with Flybe today or in the future, please DO NOT TRAVEL TO THE AIRPORT unless you have arranged an alternative flight with another airline."
The notice said the airline wouldn't be able to assist passengers who were flying with Flybe directly in finding alternative flights.
However, passengers with a Flybe booking sold by an intermediary were urged to get in touch directly with the relevant airline for assistance with making alternative arrangements. In its notice, the airline announced that joint administrators had been appointed.
BBC News reported that a passenger received an email from Flybe just after 3 a.m local time saying his flight had been canceled.
Paul Smith, consumer director at the UK Civil Aviation Authority (CAA), said in a statement on the CAA's website: "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."
The statement added: "We urge passengers planning to fly with this airline not to go to the airport as all Flybe flights are canceled. For the latest advice, Flybe customers should visit the Civil Aviation Authority's website or our Twitter feed for more information."
Flybe operated regional flights in the UK, as well as a few European destinations, including France and the Netherlands.
In October 2020, it was purchased by Thyme Opco, a firm controlled by Cyrus Capital, and the airline resumed flights in April last year.
Flybe didn't immediately respond to a request for comment by Insider.
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