Virgin Atlantic warned of booking complications as IT systems were shut down overnight on Saturday for an upgrade.
The work was scheduled to be carried out between midnight and 5am on Sunday morning.
Customers were unable to book flights or change reservations on the Virgin Atlantic website, the carrier’s mobile app, via travel agents or through the airline’s customer-service centre.
People who were due to be flying during the upgrade period were advised to check-in online at Delta.com, Virgin Atlantic’s joint venture partner.
The airline also increased the number of staff at its customer service centre and at airports to help customers requiring any additional support.
“Following the upgrade, an initial period of adjustment is expected and some booking and check-in functions may still be limited,” the carrier said.
“However, Virgin Atlantic expects its new system to deliver significant benefits for its customers.”
A spokeswoman said the upgrade was completed early yesterday morning and the new website is up and running with online check in.