A statement posted on Rex's website on Tuesday said Regional Express Holdings Limited and a number of its subsidiaries under the Rex Group have entered voluntary administration.
Ernst & Young Australia have been appointed administrators.
The statement said regional Saab 340 flights were unaffected and will continue to operate, but domestic 737 services have been grounded with Virgin Australia offering impacted Rex passengers free rebooking.
"Flights between major airports have been cancelled, with the Rex Group's domestic fleet of Boeing 737 aircraft all grounded," the statement said.
"Affected customers are being contacted directly by Rex."
The statement came after the carrier's expansion into major city routes was been questioned by the prime minister.
A trading halt followed reports Rex called in consultancy firm Deloitte to review its books. (Luis Ascui/AAP PHOTOS)
Rex began servicing Sydney-to-Melbourne, one of the busiest routes in the world, in 2021.
Rex's website showed no available flights between the capital cities from Wednesday.
Regional Express's shares went into a trading halt on the Australian stock exchange following recent boardroom turbulence and multimillion-dollar losses.
The trading halt followed reports Rex called in consultancy firm Deloitte to review the airline's books.
Shares in Rex have been falling as the airlines battles rising costs. (Dean Lewins/AAP PHOTOS)
Earlier Transport Minister Catherine King said the government was in contact with the airline.
"Regional aviation is incredibly important ... aviation is a pretty tough business, and we're seeing that," she told ABC News.
"Obviously we saw that with Bonza folding. We don't want to see Rex fold as well, so we're keeping a fairly close eye on it."
Rex employs about 2000 people.
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