JAL says it has suspended ticket sales for all services on Thursday following the incident.
Japan Airlines (JAL) has said it has been hit by a cyber crisis, which is causing some flight delays.
The airline has been experiencing “disruptions to external communications systems” since shortly after 7:30am local time (23:30 GMT, Wednesday), JAL said on Thursday.
JAL temporarily shut down the router that caused the disruption shortly after 9am and is currently “checking the status of the system”, the Tokyo-based airline said.
“We've realized the scale of the situation and we're looking at how the system works,” JAL said.
The airline added that there were delays to domestic and international flights and that it had suspended ticket sales for all operations scheduled for Thursday.
More than a dozen flights were delayed at several Japanese airports, but there were no major cancellations, public broadcaster NHK said.
All Nippon Airways, JAL's main rival, said it was not affected by the cyber incident and that operations were normal.
American Airlines briefly grounded all flights on Christmas Eve after experiencing technical problems with its network.