Virgin Blue cancelled 16 flights this morning as it upgrades its systems to mend a computer glitch.
The airline's web and kiosk check-in services were suspended on Tuesday and are expected to be back on deck by Thursday.
Customers can't make new bookings or change or cancel an existing booking while the reservation system is offline.
Web check-in, Kiosk check-in and Check-mate are closed until 2am on Thursday.
A spokeswoman for the airline said it had announced the 16 flight cancellations on Saturday but a few people may still not know about them.
Virgin staff will be at airports to assist them, she said.
Passengers are being urged to check in for domestic flights two hours before scheduled departure time and three hours for international journeys.
An IT glitch last week sent the airline's computer system into meltdown.
Virgin Blue staff nationwide had to process check-ins by hand and flights were cancelled.
Thousands of passengers were delayed on Sunday and Monday last week and many were put up in hotels overnight.